Selina Concise Solutions for ICSE Class 6 Physics Chapter 4 Simple Machines

Synposis

1. Work is said to be done when a force applied on a body moves it. If the body does not move on applying a force on it, no work is done by the force.
2. The capacity of doing work is called energy.
3. A machine is a device which helps us to do work more easily.
4. A machine enables us to apply a less effort for a load greater than the effort or to apply the effort at convenient point and in a desired direction.
5. Some machines are simple and some are complex.
6. The mechanical advantage of a machine is the ratio of the load to the effort, i.e.,
7. Mechanical advantage = Load / Effort
8. Smaller the effort required for a certain load, greater is the mechanical advantage of the machine.
9. The efficiency of a machine is the ratio of the useful work done on the load by the machine to the work put into the machine by the effort, i.e.
10. Efficiency = Work output / Work input
11. The efficiency of an ideal machine is 1 (or 100 per cent).
12. The efficiency of an actual machine is less than 1 because some part of the work put into the machine is lost in overcoming the friction between the moving parts of the machine.
13. A lever is a simple machine which we most commonly use in our daily life. It is a rod which can turn about a fixed point called the fulcrum.
14. The mechanical advantage of a lever is equal to the ratio of the effort arm to the load arm, i.e. Mechanical advantage of a lever = Effort arm / Load arm
15. The levers are of three kinds :
16. Class I levers which have fulcrum in between the load and the effort.
17. Class II levers which have load in between fulcrum and the effort.
18. Class III levers which have effort in between the fulcrum and the load.
19. The mechanical advantage of class I lever can be 1, more than 1 or less than 1.
20. The mechanical advantage of class II levers is always more than 1.
21. The mechanical advantage of class III levers is always less than 1.
22. A pulley is a simple machine which is used for raising a load up by applying the effort downwards.
23. The mechanical advantage of an ideal pulley is 1. In an actual pulley, due to friction, the mechanical advantage is less than 1 (i.e., the effort is more than the load).
24. The pulley allow us to apply the effort downwards which is a convenient direction.
25. The wheel and axle is a simple machine having a wheel and an axle. The linear motion of axle is obtained by rotating the wheel so as to reduce friction. Example: Steering wheel, screw drivers, water tap etc.
26. An inclined plane is a simple machine which is used to move a load up with a less effort. It is a sloping (or slanting) surface.
27. Less the slope of the inclined plane, less is the effort needed to push a load up.
28. The mechanical advantage of an inclined plane is greater than 1 (i. e. a less effort is required to push a heavy load up an inclined plane).
29. A wedge is a sharp edge formed by joining the two inclined planes together. Example: nail, knife, axe, plough etc.
30. A screw is a modified form of an inclined plane.
31. A screwjack is a simple machine having a combination of a screw and a lever. It is used to lift the heavy vehicles such as cars, trucks, buses etc.
32. Machines are used for our convenience. Therefore, we should take proper care of a machine by painting the machine parts to avoid rusting, lubricating its parts to reduce friction etc. This increases the life span of the machine.

Test yourself

A. Objective Questions

1. State whether the following statements are True or False.

(a) A boy does work while pushing a wall.
Answer: False
In physics, work requires the object to move in the direction of the force. Since the wall does not move despite the boy's effort, the work done is zero.
Teacher's Tip: Remember the formula W = F x d. If distance (d) is zero, work (W) is always zero.
Exam Tip: For questions about work, always check if the object actually changed its position.

(b) A machine performs work by itself.
Answer: False
A machine is just a tool that needs external energy or effort to operate. It transforms or transfers energy but cannot create it to work on its own.
Teacher's Tip: Think of a bicycle; it won't move until you start pedaling!
Exam Tip: Always state that machines require an "input" to provide an "output."

(c) In an ideal machine, work done on load is equal to the work done by effort.
Answer: True
An ideal machine is a theoretical concept where there is zero energy loss due to friction. In such a case, the energy you put in is exactly equal to the energy you get out.
Teacher's Tip: Ideal = Perfect, and perfection in machines means 100% efficiency.
Exam Tip: Mention that ideal machines do not exist in the real world because of friction.

(d) All levers are force multipliers.
Answer: False
While Class II levers always multiply force, Class III levers are actually speed multipliers. Class I levers can be either depending on the position of the fulcrum.
Teacher's Tip: Class 3 levers trade force for speed, like when you use a hockey stick.
Exam Tip: Remember that "force multipliers" have a mechanical advantage greater than 1.

(e) A pulley changes the direction of force.
Answer: True
A single fixed pulley allows you to pull downward to lift an object upward. This change in direction makes it easier to use your own body weight as effort.
Teacher's Tip: It's much easier to pull down on a rope than to lift a heavy bucket straight up!
Exam Tip: Use the term "convenient direction" when explaining the benefit of a fixed pulley.

(f) An inclined plane always has the mechanical advantage more than 1.
Answer: True
An inclined plane allows you to lift heavy loads using less effort by moving them over a longer distance. Because the effort required is always less than the load, the MA is always greater than 1.
Teacher's Tip: A longer ramp makes the climb easier but the walk longer.
Exam Tip: Mechanical Advantage (MA) is > 1 when the effort is smaller than the load.

2. Fill in the blanks

(a) The useful work done by an actual machine is always less than the work done on the machine.
Answer: less
In real life, some input energy is always wasted as heat due to friction between moving parts. This means the work coming out of the machine is never quite as much as what went in.
Teacher's Tip: Friction is like a "tax" on energy; it takes away a little bit of work every time.
Exam Tip: Use the term "efficiency" to describe the relationship between these two types of work.

(b) In class II levers, the load is in between fulcrum and effort.
Answer: effort
In this arrangement, the effort arm is always longer than the load arm. A classic example of this is a wheelbarrow or a nutcracker.
Teacher's Tip: Use the acronym "FLE" for middle parts: 1-Fulcrum, 2-Load, 3-Effort.
Exam Tip: Drawing a quick linear diagram (F---L---E) helps visualize the lever class correctly.

(c) The mechanical advantage of class III lever is always less than 1.
Answer: less than 1
In Class III levers, the effort is applied closer to the fulcrum than the load is. This means you need more force, but the load moves a much greater distance or speed.
Teacher's Tip: Think of tweezers; you press hard in the middle to move the tips a tiny bit.
Exam Tip: When MA < 1, the machine acts as a speed multiplier, not a force multiplier.

(d) A pulley is used to change the direction of effort.
Answer: the direction of effort
Changing the direction allows a person to use their weight effectively by pulling down. This is much more ergonomic and safer than lifting a heavy load directly against gravity.
Teacher's Tip: Pulling down lets you use gravity to your advantage!
Exam Tip: Always specify that a "fixed" pulley is primarily used for this purpose.

(e) Mechanical advantage of an inclined plane is always greater than 1.
Answer: greater than 1
The slope of the plane helps support part of the weight of the load. This reduces the amount of force you need to apply to move the object to a higher level.
Teacher's Tip: Steep ramps are hard; gentle ramps are easy because MA is higher.
Exam Tip: The formula for MA of an inclined plane is Length / Height.

3. Match the following
Column A
(a) Needle
(b) Door knob
(c) Ramp
(d) Lemon crusher
(e) See saw

Column B
(i) class II lever
(ii) inclined plane
(iii) Class I lever
(iv) wheel and axle
(v) wedge

Answer:
(a) Needle - (v) wedge
(b) Door knob - (iv) wheel and axle
(c) Ramp - (ii) inclined plane
(d) Lemon crusher - (i) class II lever
(e) See saw - (iii) Class I lever
These everyday objects are examples of the six basic simple machines. By identifying their structure, we can understand how they help us apply force or move things.
Teacher's Tip: Look for where the "hinge" or "slope" is to identify the machine type.
Exam Tip: Practice categorizing common tools; it's a frequent question in science exams.

4. Select the correct alternatives

(a) For an ideal machine, the efficiency is
1. greater than unity
2. less thaii unity
3. equalto unity
4. depends on the value of load
Answer: 3. equal to unity
"Unity" means 1 or 100%. In an ideal machine, work output is exactly equal to work input, so the ratio is 1.
Teacher's Tip: Unity is just a math word for "One."
Exam Tip: In real machines, efficiency is always "less than unity" because of friction.

(b) Mechanical advantage of a machine is defined as:
1. Load X Effort
2. Load / Effort
3. Load + Effort
4. Effort / Load
Answer: 2. Load / Effort
MA tells us how many times a machine multiplies our input force. If a machine has an MA of 5, it means we can lift a load five times heavier than the effort we apply.
Teacher's Tip: Remember the formula as "L over E" (Like the letters in LEver).
Exam Tip: Check your units; MA is a ratio and has no unit (like kg or N).

(c) The mechanical advantage of a lever is equal to:
1. Load arm / Effort arm
2. Effort arm / Load arm
3. Load arm + Effortarm
4. Load ann - Effort arm
Answer: 2. Effort arm / Load arm
This ratio relates the physical lengths of the lever parts. To make a lever more powerful, you want a very long effort arm and a short load arm.
Teacher's Tip: To lift a heavy load, keep the load close to the fulcrum!
Exam Tip: Make sure you don't flip the fraction; it's always Effort arm over Load arm.

(d) A pulley is used because it
1. has the mechanical advantage greatcr than one
2. has 100% efficiency
3. helps to apply the force in a convenient direction
4. requires more effort to raise a less load.
Answer: 3. helps to apply the force in a convenient direction
A single fixed pulley doesn't reduce the force needed, but it changes the pull from upward to downward. This allows you to use your body weight to help lift the load.
Teacher's Tip: It's all about making the job easier on your back!
Exam Tip: A single fixed pulley has an MA of 1, so it's not a force multiplier.

(e) Wheel is used with axle because
1. sliding friction is less than the roffing friction
2. rolling friction is less than the sliding friction
3. they work as the inclined plane
4. They help us to change the direction of force.
Answer: 2. rolling friction is less than the sliding friction
Wheels allow parts to roll over surfaces rather than dragging them. Rolling friction is much smaller than sliding friction, which makes movement much smoother and requires less energy.
Teacher's Tip: This is why it's easier to push a wagon than to drag a box of the same weight!
Exam Tip: Use the term "rolling friction" specifically to explain why wheels are efficient.

B. Short/Long Answer Questions

Question 1: When is work said to be done by a force?
Answer: Work is said to be done when a force moves an object through a distance in its own direction.
If you push a wall and it doesn't move, you might get tired, but no "work" is done in the eyes of physics. There must be both a force applied and a resulting movement in the same direction.
Teacher's Tip: No movement = No work. Simple as that!
Exam Tip: Always mention that movement must be in the "direction of the force."

Question 2: What is energy?
Answer: Energy: The ability or capacity to do work is called energy.
Energy exists in many forms like heat, light, and motion. When work is done, energy is transferred from one object or form to another.
Teacher's Tip: Think of energy as the "fuel" that allows work to happen.
Exam Tip: The S.I. unit for energy is the Joule (J), just like work.

Question 3: What do you understand by a machine?
Answer: Machine: A machine is a device that allows us to do work with less effort. Machines make our work easier to do. Machines have made our lives comfortable and faster.
A machine doesn't do the work for you, but it makes the task more manageable by multiplying force or changing its direction. Even something as simple as a spoon or a hammer is considered a machine.
Teacher's Tip: Machines aren't just robots; they are any tool that helps your effort.
Exam Tip: Define a machine as a "force multiplier" or "direction changer" to show deeper understanding.

Question 4: What is the principle on which a machine works ?
Answer: Principle of a Machine: The work output of a machine is equal to the work input.
This principle applies strictly to an "ideal machine" where no energy is lost. In reality, work output is always slightly less than work input due to friction and heat.
Teacher's Tip: Energy cannot be created or destroyed, only transformed.
Exam Tip: Always clarify if you are talking about an "ideal" or an "actual" machine when stating this principle.

Question 5: State two functions of a machine.
Answer: Various functions that a machine can perform are:
1. Changing the direction of applied force - Example: When a flag is hoisted with the help of a pulley.
2. Changing the magnitude of applied force - Example: Bottle opener multiplies the applied force and much less effort is required to open the cap.
3. Applying force at a convenient point - Example: In a pair of scissors, the input force is applied at the handle of the scissors which cuts the paper at the other end of the blade.
4. Changing the speed of an object - Example: While riding a bicycle, force is applied on pedals which multiplies the speed.
Machines act as versatile assistants that adapt the force we have to the task at hand. By changing either the strength, direction, or speed of our effort, they make impossible tasks easy.
Teacher's Tip: Use the "4 Cs": Change direction, Change magnitude, Convenient point, Change speed.
Exam Tip: Providing a real-world example with each function will gain you extra points.

Question 6: Name six simple machines. Give an example of each machine.
Answer: The Simple Machines and there examples are as follows:
1. The lever: Examples are a crow bar, claw hammer, a pair of pilers etc.
2. The Inclined plane: Examples are ramp, staircase, hilly roads etc.
3. The wedge: Examples are knife, axe, plough, nail etc.
4. Screw: Examples are A screw.
5. The wheel and axle: Examples are steering wheel of a car, bicycle pedal etc.
6. The pulley: Examples are a pulley used in raising a load.
These six devices are the building blocks of every complex piece of technology in the world. Even a car or a computer contains these fundamental mechanical concepts in its internal parts.
Teacher's Tip: Try to find one of each machine in your own kitchen!
Exam Tip: Be sure you can describe the basic shape of each machine for identification questions.

Question 7: Define the term ‘work input’ and ‘work output’ in relation to a machine.
Answer: Work input is work done on a machine equal to the effort force times the distance through which the force is applied.
Work output is work that is done by a machine equals resistance force times the distance through which the force applied.
For an ideal machine, the work output is equal to the work input i. e. the efficiency.
Work input represents the "cost" of the operation, while work output represents the "benefit" or useful result. In real machines, we want these two numbers to be as close as possible.
Teacher's Tip: Input is what YOU do; Output is what the MACHINE does.
Exam Tip: Remember the formula Work = Force x Distance for both input and output calculations.

Question 8: Explain the term mechanical advantage of a machine.
Answer: The mechanical advantage of a machine is the ratio of the load to the effort. In other words Mechanical advantage (M.A.) = Load (L) / Effort (E).
MA measures how many times the machine makes your task easier by multiplying your force. A high MA means you can lift very heavy objects with very little physical strength.
Teacher's Tip: MA is like a "Multiplier" for your muscles.
Exam Tip: MA does not have a unit because it is a ratio of two similar quantities.

Question 9: Define the term efficiency of a machine.
Answer: The ratio of the work done by the machine to the work done on the machine is called efficiency of a machine.
Efficiency = Output energy / Input energy
(Work done by a machine is called the output energy and the work done on a machine is called the input energy.)
Efficiency tells us how much energy is being used productively versus how much is wasted. We usually multiply this decimal by 100 to express it as a percentage.
Teacher's Tip: High efficiency means the machine is "smart" and wastes very little energy.
Exam Tip: For actual machines, efficiency is always < 1 (or < 100\%).

Question 10: What is an ideal machine?
Answer: A machine is which no part of the work done on the machine is wasted, is called an ideal or perfect machine. Thus, for an ideal machine, the work output is equal to the work input, i.e., the efficiency of an ideal machine is 1 (or 100 per cent).
This is a perfect machine with no friction and no heat loss. While it's impossible to build one, scientists use this model to study how machines should work in theory.
Teacher's Tip: "Ideal" is just another way to say "Perfect."
Exam Tip: State clearly that in an ideal machine, Work Output = Work Input.

Question 11: Can a machine have an efficiency of 100% ? Give a reason to support your answer.
Answer: Efficiency of a machine is always less than 100% as output energy is always less than the input energy, because some energy is lost to overcome friction.
No machine is perfectly smooth, so moving parts always rub against each other and generate heat. This wasted heat energy is why we can never get 100% of our input back as useful work.
Teacher's Tip: Friction is the "Energy Thief" in every machine.
Exam Tip: Mention "friction" and "heat loss" as the specific reasons for lower efficiency.

Question 12: A machine is 75% efficient’. What do you understand by this statement ?
Answer: If a machine is 75% efficient, it means that 75% of the work input to the machine is obtained as the useful work output. The remaining 25% of the work input has been lost in overcoming the friction.
This means for every 100 units of energy you give the machine, only 75 actually do the job. The rest of the energy is wasted, usually turning into noise or heat.
Teacher's Tip: Efficiency tells you what percentage of your effort "survives" to do the task.
Exam Tip: Always explain both what is "kept" (75%) and what is "lost" (25%).

Question 13: What is a lever ?
Answer: Lever: A lever is a simple rigid bar which is free to move around a point called fulcrum.
It is one of the oldest simple machines used to lift heavy weights with minimal force. The distance from the fulcrum determines how much the force is multiplied.
Teacher's Tip: A seesaw is the most common example of a lever in action.
Exam Tip: Include the three key components in your definition: Fulcrum, Load, and Effort.

Question 14: Describe three orders of levers giving an example of each. Draw neat diagrams showing the positions of fulcrum, load and effort in each kind of lever.
Answer: The levers are of three kinds :
Class I levers which have fulcrum in between the load and the effort. Eg. See-Saw.
Class II levers which have load in between the fulcrum and the effort. Eg. Nut-Cracker.
Class III levers which has effort in between the fulcrum and the Load. Eg. Forceps.
Levers are classified based on which part—Fulcrum, Load, or Effort—is in the middle. Changing this order completely changes whether the lever makes you stronger or faster.
Teacher's Tip: Remember the middle point with the word "FLE" (1-Fulcrum, 2-Load, 3-Effort).
Exam Tip: When drawing diagrams, use arrows for Load/Effort and a triangle for the Fulcrum.

Question 15: What do you mean by the mechanical advantage of a lever ?
Answer: The mechanical advantage of a lever is equal to the ratio of the effort arm to the load arm. This is also called the principle of a lever.
The longer your effort arm is compared to the load arm, the easier it is to lift the weight. This is why long wrenches are better at turning tight bolts than short ones.
Teacher's Tip: "Give me a lever long enough... and I shall move the world!"
Exam Tip: Write the formula MA = Effort Arm/Load Arm to get full marks.

Question 16: Which class of lever has the mechanical advantage always more than 1 ? Give an example.
Answer: The mechanical advantage of class II levers is always more than 1. Example - Nut cracker, wheel barrow, bottle opener etc.
In Class II levers, the effort is always further from the fulcrum than the load is. Since the effort arm is always longer than the load arm, the MA will always be greater than 1.
Teacher's Tip: Class 2 is the "Force Multiplier" class.
Exam Tip: Mention that the Effort Arm is always larger than the Load Arm in this class.

Question 17: Which class of lever has the mechanical advantage always less than 1 ? Give an example.
Answer: The mechanical advantage of class III levers is always less than 1. Example: a pair of tongs, sugar tongs, knife, forceps etc.
Because the effort is in the middle, the effort arm is always shorter than the load arm. While this requires more force, it allows the tip of the tool to move very fast.
Teacher's Tip: Class 3 is about "Speed and Precision," not strength.
Exam Tip: Explain that MA < 1 means the machine is a "Speed Multiplier."

Question 18: Give one example of class I lever in each case where the mechanical advantage is 1. more than 1 2. equal to 1 3. less than 1.
Answer:
1. more than 1: Load arm of pliers
2. equal to 1: See - saw
3. less than 1: The load arm of a pair of scissors.
In Class I levers, the fulcrum is in the middle, but it doesn't have to be exactly in the center. Moving the fulcrum toward the load makes MA > 1, while moving it toward the effort makes MA < 1.
Teacher's Tip: The position of the fulcrum is the "volume knob" for a Class 1 lever's power.
Exam Tip: Be specific with examples; a seesaw is only MA=1 if both people sit at equal distances.

Question 19: Name the class to which the following levers belong:
(a) A pair of scissors (b) a lemon squeezer (c) a nut cracker (d) a pair of sugar tongs
(e) a beam balance (f) an oar rowing a boat (g) a wheel barrow (h) a see saw
(i) a pair of pilers (j) a crow bar
Answer:
(a) A pair of scissors - Class I lever
(b) a lemon squeezer - Class II lever
(c) a nut cracker - Class II lever
(d) a pair of sugar tongs - Class III lever
(e) a beam balance - Class I lever
(f) an oar rowing a boat - Class I lever
(g) a wheel barrow - Class II lever
(h) a see saw - Class I lever
(i) a pair of pilers - Class I lever
(j) a crow bar - Class I lever
Categorizing these tools helps us understand how they balance force and distance. Most heavy-duty tools are Class I or II, while precision tools like tongs are Class III.
Teacher's Tip: Visualize where the "push," the "load," and the "hinge" are for each tool.
Exam Tip: If you get stuck, draw a quick sketch and find what's in the middle (FLE).

Question 20: The diagram given below shows the three kinds of levers. Name the class of each lever and give one example of each class.
Answer:
Class I Lever: Fulcrum is in the middle. Examples : a see saw, a pair of scissors, a pair of pilers, crow bar, common balance, spoon opening the lid of a tin can, handle of a hand pump.
Class II Lever: Load is in the middle. Examples : nut cracker, wheel barrow, paper cutter, mango, lemon squeezer, bottle opener.
Class III Lever: Effort is in the middle. Examples : a pair of tongs, sugar tongs, knife, forceps, forearm of a person holding a load, spade for lifting soil or coal.
This classification system is the standard way engineers and scientists talk about tools. Each class has a specific mechanical advantage that makes it suitable for different kinds of jobs.
Teacher's Tip: Use the middle component to name it: 1st=F, 2nd=L, 3rd=E.
Exam Tip: Don't just name the class; always provide an example as requested by the question.

Question 21: Draw diagrams to illustrate the positions of fulcrum, load and effort, in each of the following: (a) a see saw (b) a beam balance (c) a nut cracker (d) a pair of forceps
Answer:
(a) a see saw: Fulcrum in middle, Loads on ends (Class I).
(b) a beam balance: Fulcrum at top center, Pans (Load/Effort) on ends (Class I).
(c) a nut cracker: Fulcrum at one end, Nut (Load) in middle (Class II).
(d) a pair of forceps: Fulcrum at hinge, fingers (Effort) in middle (Class III).
Visualizing these components helps us calculate the mechanical advantage of each tool. The position of the fulcrum is always the key anchor point for any lever diagram.
Teacher's Tip: Use "F" for fulcrum, "L" for load, and "E" for effort in your sketches.
Exam Tip: Label your diagrams clearly; a drawing without labels often loses half the marks.

Question 22: How can you increase the mechanical advantage of a lever ?
Answer: The mechanical advantage of a lever can be increased by increasing the effort arm or reducing the load arm.
By making the handle longer or moving the weight closer to the pivot point, you multiply your force. This allows you to lift much heavier objects than you could otherwise.
Teacher's Tip: To be more powerful, grab the lever further away from the hinge!
Exam Tip: Mention that MA = Effort Arm/Load Arm to mathematically justify your answer.

Question 23: How does the friction at the fulcrum affect the mechanical advantage of the lever ?
Answer: Friction at the fulcrum reduces the mechanical advantage.
Friction creates a backward force that works against your effort. Because some of your strength is wasted overcoming this friction, the effective power of the lever drops.
Teacher's Tip: A squeaky hinge is a sign of energy being lost to friction!
Exam Tip: State that friction also reduces the efficiency of the machine.

Question 24: State three differences between the three classes of levers.
Answer:
Class I: Fulcrum is in between load and effort. MA can be <1, 1, or >1. Effort and load move in opposite directions.
Class II: Load is in between fulcrum and effort. MA is always >1. Effort and load move in the same direction.
Class III: Effort is in between fulcrum and load. MA is always <1. Effort and load move in the same direction.
The core difference is the relative positions of the three parts, which dictates how the force is multiplied. These differences determine whether the lever is used for strength, balance, or speed.
Teacher's Tip: Remember the middle points: 1st=F, 2nd=L, 3rd=E.
Exam Tip: Tabulating your answer is the best way to present differences clearly.

Question 25: What is a pulley ?
Answer: Pulley: It is a flat circular disc with a groove in its edge and a rope passing through the groove. It is capable of rotating around a fixed point passing through its central axis called axle.
A pulley works by looping a rope or cable over a wheel. It allows us to move loads by pulling in a direction that is most comfortable for our muscles.
Teacher's Tip: A pulley is like a rotating "circle-lever" with an infinite arm.
Exam Tip: Don't forget to mention the "groove" as it keeps the rope from slipping off.

Question 26: What is the mechanical advantage of an ideal pulley ?
Answer: In an ideal pulley, the effort applied is equal to the load to be lifted. i.e. Effort = Load. Mechanical advantage = Load / Effort = 1.
An ideal fixed pulley doesn't make the object lighter to lift, it just changes the pull direction. The MA is exactly 1 because the distance the rope is pulled equals the distance the load rises.
Teacher's Tip: Ideal means "perfect world" with no friction.
Exam Tip: If MA = 1, the machine does not multiply force; it only changes direction.

Question 27: The mechanical advantage of an actual pulley is less than 1. Give a reason. What is the justification for using the pulley then ?
Answer: In an actual pulley due to friction, the mechanical advantage is less than 1 (i.e. the effort is more than the load). The reason for using the pulley when its mechanical advantage is equal to 1 or less than 1 is that the pulley allows us to apply the effort downwards i.e. in a convenient direction. To raise a load directly upwards is difficult. But with the help of a pulley, the effort can be applied in the downward direction to move the load upwards. One can hang on it to make use of his own weight also in order to apply the effort.
We use it because pulling down is much more ergonomic than lifting up. It allows us to use our body's entire weight as part of the "effort," making the task feel much easier despite the friction loss.
Teacher's Tip: Sometimes a more "convenient" job is better than a "smaller" force.
Exam Tip: The "change in direction" is the primary justification for using a fixed pulley.

Question 28: Draw a neat labelled diagram showing a pulley being used to lift a load. How are load and effort related in an ideal situation?
Answer: To raise a load, the load is attached to one end of the string and the effort is applied at the other end by pulling it is downward direction. In an ideal situation, Load = Effort.
The rope transfers your pull directly to the object on the other side. Because the rope doesn't stretch or break in an ideal model, every inch you pull is an inch the load moves.
Teacher's Tip: Load and Effort are "twin partners" in an ideal fixed pulley.
Exam Tip: Label the "Load," "Effort," "String," and "Pulley" clearly in your drawing.

Question 29: What is an inclined plane? What is its use ? Give two examples where ¡t is used.
Answer: An inclined plane is a rigid sloping surface over which heavy loads can be raised or lowered to a certain height or depth. The mechanical advantage of an inclined plane is the ratio of the length of the plank to the vertical height of the load raised. Its value is greater than one. Therefore, an inclined plane acts as a force multiplier. Thus, it can be used to lift heavy loads. Example : If a heavy box needs to be loaded on a lorry, it is far easier to push it over an inclined plane than to lift it up. Steeper the inclined plane, greater will be the effort required to push up the load. Sloping ramps, flyovers, roads on hills and staircases are all examples of inclined planes.
It trades distance for effort; by moving an object along a long slope, you need much less force than lifting it straight up. This is why wheelchair ramps are long and gentle rather than short and steep.
Teacher's Tip: A ramp is just a "slanted floor" that helps your muscles.
Exam Tip: MA of an inclined plane = Length of slope / Height.

Question 30: What is a screw ? Give two examples.
Answer: A screw is a simple machine which appears like an inclined plane wound around a rod with a pointed tip. Examples : ajar lid, a drill.
Think of it as a spiral ramp that converts rotational motion (turning) into linear motion (moving in or out). This mechanical advantage allows screws to hold things together with immense force.
Teacher's Tip: A screw is just a "spiral ramp" for a tiny ant to walk up!
Exam Tip: Mention that it is a modified form of an "inclined plane."

Question 31: What is wheel and axle ? Give two examples.
Answer: The wheel and axle is a simple machine having a wheel and an axle. The linear motion of axle is obtained by rotating the wheel so as to reduce friction. Example: Steering wheel, screw drivers, water tap etc.
When you turn the large wheel, the small axle turns with it. Because the wheel travels a longer distance, the axle exerts a much stronger force on whatever it is connected to.
Teacher's Tip: Turning a big circle to rotate a small rod makes you stronger!
Exam Tip: A door knob is a classic example of a wheel and axle machine.

Question 32: How does a wheel help in moving the axle ?
Answer: Wheel-and-axle arrangement consists of two cylinders of different diameters joined together such that if one is made to rotate, the other also rotates. The axle is a cylindrical rod fixed to the centre of a circular disc-like object called the wheel. This machine acts as a speed multiplier device. In riding a bicycle, when we apply force on the wheel (by pedal), the fixed axle rotates with it easily. This force that turns the axle produces a much larger movement of the wheel.
The wheel acts as a lever that is constantly rotating. By applying effort to the large radius of the wheel, you create a powerful torque on the axle.
Teacher's Tip: Think of the wheel as a lever that never ends.
Exam Tip: Mention "different diameters" as the key to how this machine works.

Question 33: What is a wedge ? Give two examples.
Answer: A wedge is a double inclined plane such that the two sloping surfaces taper to form either a sharp edge or a pointed edge. Examples : A knife, an axe, a chisel. In some special cases, the number of inclined planes used can be more than two as well. In such cases, the sloping surfaces generally taper to form either a very sharp or a pointed edge to split or pierce materials. Pins, nails and needles are examples of pointed wedges. The front end of a boat is shaped like a wedge so that it can easily cut across the flowing water. The wedge works on a principle of an inclined plane.
A wedge changes a downward "push" into a sideways "splitting" force. This is why a sharp knife cuts through food so easily—it concentrates your effort on a tiny edge and pushes the material apart.
Teacher's Tip: A wedge is just two ramps put back-to-back.
Exam Tip: Mention "splitting" or "piercing" as the primary uses of a wedge.

Question 34: Name the machine to which the following belong : 1. Beam balance 2. Lemon crusher 3. Sugar tongs 4. Ramp 5. Door knob 6. Needle
Answer:
1. Beam balance - A lever (lever of class I)
2. Lemon crusher - A lever (lever of class II)
3. Sugar tongs - A lever (lever of class III)
4. Ramp - An inclined plane
5. Door knob - Wheel and axle
6. Needle - Wedge
Understanding which simple machine makes up a tool helps us predict how to use it correctly. Every complex device, from a car to a sewing machine, is just these simple parts put together.
Teacher's Tip: Categorizing tools is like sorting your mechanical toolbox.
Exam Tip: For levers, always specify the "class" (I, II, or III) to show full mastery.

Question 35: What care would you take to increase the life span of a machine which you use ?
Answer: Taking care of machines: Some of the ways in which machines should be cared for are given below :
1. Machines should be kept in a clean environment, which is free from dust and moisture.
2. When not in use, machines should be kept covered to prevent collection of dust on them.
3. Machines made of iron should be protected from rust by coating them with paint.
4. The moving parts of a machine should be regularly oiled with a good-quality machine oil to reduce friction and wear and tear. The above care of machines increases their life.
Good maintenance prevents "energy theft" from friction and "part theft" from rust. By keeping them clean and lubricated, you ensure they work efficiently for many years.
Teacher's Tip: Oil is to a machine what water is to a plant—it keeps it healthy!
Exam Tip: Mention "rust prevention" and "friction reduction" as the two main goals of machine care.

Question 36: Select the correct statement :
(a) A wheel barrow is a lever of class I.
(b) The efficiency of a machine is always 100%
(c) Friction in moving parts of a machine reduces its efficiency.
(d) No lever has the mechanical advantage greater than 1.
(e) It is easier to lift a load vertically up than to push it along an inclined plane.
(f) A screw is made by two inclined planes placed together.
Answer: (c) Friction in moving parts of a machine reduces its efficiency.
Friction converts useful work into wasted heat energy. Therefore, the higher the friction, the lower the work output will be compared to the input.
Teacher's Tip: Friction is always the "efficiency killer" in any machine.
Exam Tip: Use this fact to explain why we lubricate machines with oil or grease.

C. Numericals

Question 1: In a machine an effort of 10 kgf is applied to lift a load of 100 kgf. What is its mechanical advantage ?
Answer: Given,
Load = 100 kgf
Effort = 10 kgf
Mechanical advantage = Load / Effort = 100 kgf / 10 kgf = 10
This means the machine multiplies your force by 10 times. You can lift something 100 kg heavy using only as much strength as it takes to lift 10 kg.
Teacher's Tip: MA is a ratio—notice how the units (kgf) cancel out!
Exam Tip: Always write "Given" values and the formula before calculating the answer.

Question 2: The mechanical advantage of a machine is 5. How much load it can exert for the effort of 2 kgf ?
Answer: Given,
Mechanical advantage = 5
Effort 2 kgf
MA = Load / Effort
Load = Mechanical advantage x Effort = 5 x 2 kgf = 10 kgf
Since the machine multiplies force by 5, your 2 kgf of effort becomes 10 kgf of pulling power. This is the definition of a force multiplier.
Teacher's Tip: Multiply MA by Effort to find how much "muscle" the machine gives you.
Exam Tip: Don't forget to include the unit "kgf" in your final answer for load.

Question 3: The mechanical advantage of a machine is 2. It is used to raise a load of 15 kgf. What effort is needed ?
Answer: Given,
Mechanical advantage = 2
Load = 15 Kgf
Mechanical advantage = Load / Effort
Effort = Load / Mechanical advantage = 15 / 2 = 7.5 kgf
With an MA of 2, you only need to push with half the force of the object's weight. So, for a 15 kgf object, you only need 7.5 kgf of effort.
Teacher's Tip: Divide the load by the MA to find your required effort.
Exam Tip: Show the division step clearly to avoid point loss for math errors.

Question 4: A lever of length 100 cm has effort of 15 kgf at a distance of 40 cm from the fulcrum at one end. What load can be applied at its other end ?
Answer: Given,
Effort = 15 kgf
Effort arm = 40 cm
Load arm = 100 cm - 40 cm = 60 cm (Note: Standard Class 1 setup)
By Principle of Lever: Load x Load Arm = Effort x Effort Arm
Load x 60 = 15 x 40
Load = 600 / 60 = 10 kgf
Alternative Calculation based on diagram provided in textbook:
MA = Effort Arm / Load Arm = 40 / 100 = 0.4
Load = MA x Effort = 0.4 x 15 kgf = 6 kgf
The ratio of the arms determines the power of the lever. In this specific setup, you are trading force for distance, so the load you can lift is smaller than the effort you apply.
Teacher's Tip: Closer to the fulcrum = More force. Further away = Less force.
Exam Tip: Always double-check if the "length of lever" includes the effort arm or is separate.

Question 5: In a lever, fulcrum is at one end at a distance of 30 cm from the load and effort is at the other end at a distance of 90 cm from the load. Find : (a) the length of load arm, (b) the length of effort arm, and (c) the mechanical advantage of the lever.
Answer: Given,
(a) Load arm = 30 cm (distance from load to fulcrum)
(b) Effort arm = distance from effort to fulcrum = 90 + 30 = 120 cm (since load is between fulcrum and effort)
(c) Mechanical advantage = Effort arm / Load arm = 120 cm / 30 cm = 4
In this Class II lever (like a wheelbarrow), the effort arm is much longer than the load arm. This creates a high MA, allowing you to lift four times more than your effort.
Teacher's Tip: Sketch the lever first to make sure you get the arm lengths right!
Exam Tip: Add the distances carefully for the effort arm; it's the TOTAL distance to the fulcrum.

ADDITIONAL QUESTIONS

Check Your Progress

Answer the following.

Question 1: What is a machine ?
Answer: Tools and objects that help us to perform the same amount of work with much less effort than if we did the work manually, are called machines. Example : lever, hammer, knife, etc.
A machine acts as a force multiplier or direction changer to simplify physical tasks. It allows humans to overcome heavy loads that would be impossible with bare hands.
Teacher's Tip: A machine is anything that makes you "Super Strong" or "Super Fast"!
Exam Tip: Always provide at least two examples when defining a scientific term.

Question 2: What do you understand by a complex machine ?
Answer: Machines such as sewing machines or cars that have more than one moving part are called complex machines.
A complex machine is essentially a combination of several simple machines working together. For example, a bicycle uses wheels, axles, levers, and pulleys simultaneously.
Teacher's Tip: Complex = Simple + Simple + Simple!
Exam Tip: Use a "car" or "sewing machine" as your standard examples for this definition.

Question 3: Name the simplest of all types of machines.
Answer: Lever
The lever is the most basic tool because it only consists of a rigid bar and a pivot point. It has been used since ancient times to move giant stones and heavy loads.
Teacher's Tip: A stick and a rock—that's all you need for the world's simplest machine!
Exam Tip: If asked why, mention that it has the fewest moving parts.

Question 4: State the principle of levers.
Answer: The principle of a lever states that the product of the load and the load arm is always equal to the product of the effort and the effort arm. Load x Load arm = Effort x Effort arm.
This is the law of equilibrium for a balanced lever. It shows that if you double the distance from the fulcrum, you only need half as much force.
Teacher's Tip: Think of it like a math seesaw: L x La = E xs Ea.
Exam Tip: Write the formula clearly after the written definition to score full marks.

Question 5: What is a Class I lever ?
Answer: In Class I levers (also called levers of first order), the fulcrum lies between the load and the effort, i.e., the load and the effort are on the opposite sides of the fulcrum. Examples : See-saw, pairs of scissors, pliers, beam balance, etc. The mechanical advantage of a Class I lever is always greater than one. These levers act as force multipliers.
This is the most common type of lever where the pivot is right in the middle area. By moving that pivot, you can decide whether you want more power or more balance.
Teacher's Tip: The "F" (Fulcrum) is the star of the show in Class 1—it's right in the center!
Exam Tip: Draw the F-L-E diagram to demonstrate the positions clearly.

Exercises

A. Tick the most appropriate answer.

1. The force applied on a machine to do work is called the
1. load 2. effort 3. efficiency 4. fulcrum
Answer: 2. effort
Effort is the muscle power or energy you personally put into the machine. The machine then takes this effort and applies it to the "load" to do the work.
Teacher's Tip: Effort is YOUR input; Load is the MACHINE'S task.
Exam Tip: Don't confuse "force" with "work"; effort is the actual push or pull.

2. If the effort lies between the fulcrum and the load, then the lever belongs to which class ?
1. Class I 2. Class II 3. Class III 4. Class IV
Answer: 3. Class III
In this class, you are pushing in the middle, and the weight is at the far end. Examples include your arm when lifting a ball or a pair of tongs.
Teacher's Tip: Remember "FLE": 1=F, 2=L, 3=E in the middle.
Exam Tip: Class III levers always have an MA < 1.

3. Which of the following is a Class II lever ?
1. Pliers 2. A beam balance 3. A nut-cracker 4. A knife
Answer: 3. A nut-cracker
In a nut-cracker, the hinge (fulcrum) is at one end, you squeeze the handles (effort) at the other, and the nut (load) is crushed in the middle. This makes it a Class II lever.
Teacher's Tip: If the "work" happens in the middle, it's Class 2.
Exam Tip: A wheelbarrow is another very common exam example for Class II.

4. A pair of scissors is an example of a/an
1. wedge 2. lever 3. inclined plane 4. screw
Answer: 2. lever
Specifically, a pair of scissors is a double Class I lever. The screw in the center acts as the fulcrum for both blades.
Teacher's Tip: Scissors are basically two seesaws joined together.
Exam Tip: Always categorize a tool by its primary simple machine type.

5. The mechanical advantage of an inclined plane is always
1. greater than 1 2. less than 1 3. equal to 1 4. zero
Answer: 1. greater than 1
Ramps are designed to make lifting easier, meaning the effort force is always smaller than the load weight. This results in an MA that is always above 1.
Teacher's Tip: A ramp wouldn't be very "simple" if it made the job harder!
Exam Tip: Connect "easier work" with MA > 1.

6. The effort required to lift a load of 800 N by using a lever having a mechanical advantage of 1.6 is
1. 1080 N 2. 240 N 3. 720 N 4. 500 N
Answer: 4. 500 N
Using the formula Effort = Load / MA, we calculate 800 / 1.6 = 500 N. The machine's MA reduces the amount of strength you actually need to use.
Teacher's Tip: 800 divided by 1.6 is the same as 8000 divided by 16.
Exam Tip: Show your division to ensure you don't lose marks for a calculation error.

7. A machine made up of two or more sloping surface is known as a
1. wedge 2. screw 3. pulley 4. lever
Answer: 1. wedge
A wedge is basically two inclined planes placed back-to-back. This creates a sharp edge that can split materials apart with great force.
Teacher's Tip: Think of an axe head; it's a "V" shape made of two slopes.
Exam Tip: Remember that a wedge is a "Force Multiplier" used for splitting.

B. State if the following statements are true or false. Correct the statement if it is false.

1. There are four types of simple machines.
Answer: False. There are six types of simple machines.
The six standard simple machines are the lever, pulley, wheel and axle, inclined plane, wedge, and screw. Together, these form the basis of all modern mechanical engineering.
Teacher's Tip: Count them on your fingers to remember all six!
Exam Tip: List all six if asked to correct this statement in an exam.

2. The load and effort can act at a single point in a lever.
Answer: False. The load and effort cannot act at a single point in a lever.
If they were at the same point, there would be no "lever arm" and therefore no mechanical advantage. A lever requires distance between the components to work its magic.
Teacher's Tip: You can't balance a seesaw if both people sit on top of each other!
Exam Tip: Mention that distance from the fulcrum is necessary for a lever to operate.

3. A screw is a special case of an inclined plane.
Answer: True
A screw is simply a very long inclined plane wrapped in a spiral around a central rod. This converts a turning motion into a very strong linear push or pull.
Teacher's Tip: Imagine walking up a spiral staircase—it's just a circular ramp!
Exam Tip: Use the term "spiral inclined plane" to describe a screw's geometry.

4. The effort required to insert a screw into wood is less than that needed to insert a nail into wood.
Answer: True
Because the screw has the mechanical advantage of an inclined plane, you trade many easy turns for a strong push into the wood. A nail requires a single, very powerful force from a hammer.
Teacher's Tip: Screws "crawl" into the wood, while nails "crash" into it.
Exam Tip: Explain that the "mechanical advantage" makes the screw easier to use.

5. A single movable pulley is a pulley that has its axis of rotation fixed.
Answer: False. A single fixed pulley is a pulley that has its axis of rotation fixed.
In a movable pulley, the pulley itself moves up and down along with the load. This movement is what allows a movable pulley to actually multiply your force.
Teacher's Tip: If it's "fixed," it's stuck in one place. If it's "movable," it travels with the weight.
Exam Tip: Remember that a fixed pulley MA = 1, while a movable pulley MA = 2.

6. A rotation spindle tap is an example of a wheel-and-axle arrangement.
Answer: True
The handle you turn is the "wheel," and the inner rod that controls the water is the "axle." Turning the large handle makes it easy to rotate the tight valve inside.
Teacher's Tip: Every time you turn a faucet, you're using a simple machine!
Exam Tip: Identify the handle as the "wheel" and the spindle as the "axle."

7. A sewing needle is a wedge type simple machine.
Answer: True
The pointed tip of a needle is a sharp wedge that pushes fabric fibers aside to make a hole. This allows the needle and thread to pass through with minimal resistance.
Teacher's Tip: Anything that "pokes" or "splits" is usually a wedge.
Exam Tip: Mention that a wedge works on the principle of an inclined plane.

8. Work done by a machine is always more than the work done on a machine.
Answer: False. Work done by a machine is always less than the work done on a machine.
No machine is perfect; energy is always lost to friction and heat. Therefore, you will never get 100% (or more!) of your effort back as useful output.
Teacher's Tip: You can't get something for nothing in physics!
Exam Tip: Use the term "energy loss" to explain why output is lower than input.

C. Answer the following in a word or two or in a sentence.

Question 1: Given an example of a Class I lever.
Answer: See-saw, pair of scissors.
In these tools, the pivot point (fulcrum) is between the effort you apply and the result you want. This is the most "balanced" of all the lever types.
Teacher's Tip: Think of a playground; the seesaw is the ultimate Class 1 lever.
Exam Tip: Providing two examples is always safer than just one.

Question 2: Which type of machine is used to squeeze a lemon ?
Answer: Class II lever.
In a lemon squeezer, the hinge is at the end, the lemon (load) is in the middle, and you press the handles (effort) at the far end. This makes it a force multiplier.
Teacher's Tip: If you're crushing something in the "belly" of the tool, it's Class 2.
Exam Tip: Specify "Class II Lever" for a complete technical answer.

Question 3: Write the relationship between mechanical advantage, load and effort.
Answer: Mechanical advantage (MA) = Load / Effort.
This ratio tells you how much "strength" the machine is adding to your effort. If the MA is high, even a weak person can lift a very heavy weight.
Teacher's Tip: MA is the "Muscle Number" of a machine.
Exam Tip: Remember that MA has no unit because the force units cancel out.

Question 4: Name the type of machine made by putting two inclined planes together.
Answer: Wedge
By joining two slopes, you create a sharp "V" shape that is perfect for cutting or splitting. An axe head or a knife blade are perfect examples of this.
Teacher's Tip: Two ramps back-to-back = one wedge.
Exam Tip: Mention that the wedge works on the principle of an inclined plane.

Question 5: Give one example of a machine used to multiply speed.
Answer: Class III lever (hockey stick, broom).
By moving your hands a small distance in the middle, the end of the stick travels a much larger distance very quickly. You trade "muscle" for "speed."
Teacher's Tip: Speed multipliers move fast, but they don't lift heavy things easily.
Exam Tip: Class III levers always have an MA < 1.

Question 6: Write the formula for calculating the efficiency of a machine.
Answer: Efficiency = Output energy / Input energy. The percentage value of efficiency of a machine is calculated as Efficiency = Output energy/Input energy x100 \%.
This formula measures how "wasteful" or "productive" a machine is. No real machine can ever reach 100\% because of friction and energy loss.
Teacher's Tip: Efficiency is like a "Grade" for how well a machine uses energy.
Exam Tip: Don't forget to multiply by 100 if the question asks for "percentage efficiency."

D. Answer the following in short.

Question 1: Explain the various functions that a machine can perform.
Answer: Various functions that a machine can perform are :
1. Changing the direction of applied force — Example : When a flag is hoisted with the help of a pulley.
2. Changing the magnitude of applied force — Example : Bottle opener multiplies the applied force and much less effort is required to open the cap.
3. Applying force at a convenient point — Example : In a pair of scissors, the input force is applied at the handle of the scissors which cuts the paper at the other end of the blade.
4. Changing the speed of an object — Example : While riding a bicycle, force is applied on pedals which multiplies the speed.
Machines act as versatile tools that modify the energy we have to fit the task we need to do. Whether it's making us stronger, faster, or simply letting us pull in a better direction, they are essential for work.
Teacher's Tip: Use the "Four Ds": Direction, Distance (speed), Drag (magnitude), and Displacement (point).
Exam Tip: Listing these four points with examples is a very common 5-mark question.

Question 2: What is the basis of classification of levers ?
Answer: Levers are classified on the basis of the relative positions of load, effort and fulcrum.
Specifically, we look at which of these three parts is located in the middle. This simple position change determines if the lever makes you stronger, faster, or more balanced.
Teacher's Tip: It's all about "Who's in the Middle?"
Exam Tip: Mention "Fulcrum, Load, and Effort" specifically in your answer.

Question 3: What is the function of a screw ? Give any one use of a screw.
Answer: A screw is a special type of an inclined plane which has a sharp and pointed tip and can be turned (using a screw driver, bolt or a jack.) It acts as a force multiplier and less effort is required to do the work. Example : Screw forced and rotated into wood travels a greater distance with less effort than a nail would. Bolt rotating inside the fixed nut and jack used to lift a car use the principle of screw.
The screw's spiral thread allows you to apply a small force over many turns to create a massive forward push. This is why screws are so much better at holding things together than nails.
Teacher's Tip: A screw is a "Spiral Ramp" for your effort.
Exam Tip: Mention that the screw jack is used to lift heavy vehicles like cars.

Question 4: Using a suitable example, describe how a machine acts as a force multiplier.
Answer: It is very difficult to open the sealed metal cap of a cold drink bottle with our bare hands. A simple machine like a bottle opener (Class II lever) multiplies the applied force and much less effort is required to open the cap. Hence, it acts as a force multiplier.
By using a long handle, the opener magnifies your muscle strength. This allows a small input from your hand to create a huge upward force on the cap.
Teacher's Tip: If the job feels "lighter" than the actual weight, the machine is multiplying force.
Exam Tip: A mechanical advantage greater than 1 (MA > 1) is the technical sign of a force multiplier.

Question 5: What do you understand by the term ‘efficiency of a machine’?
Answer: The ratio of the work done by the machine to the work done on the machine is called efficiency of a machine. Efficiency = Output energy / Input energy. [Work done by a machine is called the output energy and the work done on a machine is called the input energy.]
Efficiency is a scorecard for energy usage. It tells you how much of your hard work is actually finishing the task versus how much is wasted rubbing against parts.
Teacher's Tip: Efficiency is "Work Out divided by Work In."
Exam Tip: Always clarify that output is *useful* work and input is *total* work.

Question 6: Mention any two methods by which we can take care of machines.
Answer: Taking care of machines : Some of the ways in which machines should be cared for are given below.
1. Machines should be kept in a clean environment, which is free from dust and moisture.
2. When not in use, machines should be kept covered to prevent collection of dust on them.
3. Machines made of iron should be protected from rust by coating them with paint.
4. The moving parts of a machine should be regularly oiled with a good-quality machine oil to reduce friction and wear and tear.
Good maintenance prevents the "Energy Thief" (friction) from slowing down your machine. It also stops "Rust" from eating away at the metal, keeping the tool strong for years.
Teacher's Tip: Clean and Oiled—that's the recipe for a happy machine!
Exam Tip: Lubrication and painting are the two most important maintenance methods to mention.

E. Answer the following in detail.

Question 1: Draw simplified diagrams by clearly showing the position of load, effort and fulcrum for Class I, Class II and Class III levers.
Answer:
Class I: Fulcrum in the middle. (Effort --- Fulcrum --- Load)
Class II: Load in the middle. (Fulcrum --- Load --- Effort)
Class III: Effort in the middle. (Fulcrum --- Effort --- Load)
Drawing these linear models helps scientists analyze how a tool will behave. The placement of these three points determines if the lever will make a job easier or faster.
Teacher's Tip: Use a straight line and the letters F, L, and E to make perfect diagrams.
Exam Tip: Ensure your labels are clear; a diagram without labels won't get full marks.

Question 2: How does a pulley make work simpler ? Differentiate between a single fixed pulley and a single movable pulley.
Answer: A pulley is a wheel or a circular disc that can rotate freely about its axle. It is used to lift heavy objects. It is neither a force multiplier nor a speed multiplier. It only changes the direction of the applied force from upwards against gravity to downwards towards gravity. There are two types of pulley systems – Single fixed pulley and single movable pulley.
Single fixed pulley: (i) This pulley has a fixed axis of rotation. (ii) The load is attached to one end of the rope. (iii) Only the direction of the force is changed, not the magnitude. (iv) The mechanical advantage of this pulley is 1. (v) Example : Used to draw water from wells.
Single movable pulley: (i) The axis of rotation of this pulley is not fixed. (ii) The load is attached to the pulley. (iii) The direction of the force as well as the magnitude of force change. (iv) The mechanical advantage of this pulley is 2. (v) Example : Used in construction cranes, weight lifting, machines in gym, etc.
Pulleys are all about making lifting ergonomic. While the fixed pulley only changes direction, the movable pulley actually cuts the force you need in half, which is a massive help for heavy lifting.
Teacher's Tip: Fixed Pulley = Direction Change. Movable Pulley = Force Split (Half the effort!).
Exam Tip: Contrast the Mechanical Advantages (MA=1 for fixed, MA=2 for movable) clearly in your answer.

Question 3: What is a wedge ? Explain the principle on which it works by giving suitable examples.
Answer: A wedge is a double inclined plane such that the two sloping surfaces taper to form either a sharp edge or a pointed edge. Examples : A knife, an axe, a chisel. In some special cases, the number of inclined planes used can be more than two as well. In such cases, the sloping surfaces generally taper to form either a very’ shaip or a pointed edge to split or pierce materials. Pins, nails and needles are examples of pointed wedges. The front end of a boat is shaped like a wedge so that it can easily cut across the flowing water. The wedge works on a principle of an inclined plane.
The wedge takes your downward push and turns it into a powerful sideways splitting force. This concentration of force on a tiny edge is what makes cutting and splitting impossible objects like logs or thick fabrics so simple.
Teacher's Tip: A wedge is just two ramps put back-to-back to make a point.
Exam Tip: Mention that the "mechanical advantage" of a wedge is what allows it to split tough materials.

Question 4: What is an inclined plane ? What is the use of an inclined plane ?
Answer: An inclined plane is a rigid sloping surface over which heavy loads can be raised or lowered to a certain height or depth. The mechanical advantae of an inclined plane is the ratio of the length of the plank to the vertical height of the load raised. Its value is greater than one. Therefore, an inclined plane acts as a force multiplier. Thus, it can be used to lift heavy loads. Example : If a heavy box needs to be loaded on a lorry, it is far easier to push it over an inclined plane than to lift it up. Steeper the inclined plane, greater will be the effort required to push up the load. Sloping ramps, flyovers, roads on hills and staircases are all examples of inclined planes.
It allows you to lift a very heavy weight using very little muscle strength, just by moving it over a longer distance. This trade-off is one of the most fundamental principles in all of mechanics.
Teacher's Tip: Longer slope = Easier push. Higher hill = Harder push.
Exam Tip: State the formula MA = Slope Length/Height to show you understand the math behind the ramp.

F. Give reasons for the following.

Question 1: Machines are able to make our work convenient.
Answer: Machines help us to perform the same amount of work with much less effort than if we did the work manually. They also make our work faster and easier by multiplying the speed or the force applied.
Without machines, tasks like lifting a car or splitting a log would be impossible for a human. Machines bridge the gap between human strength and the massive forces needed for modern life.
Teacher's Tip: Machines are "Strength Magnifiers" for humans.
Exam Tip: Mention "force multiplication" and "changing direction" as the reasons for convenience.

Question 2: The efficiency of a machine is always less than 100%.
Answer: Efficiency of a machine is always less than 100% as output energy is always less than the input energy, because some energy is lost to overcome friction.
There is no such thing as a perfectly frictionless surface. Every time two parts rub together, some of your input work turns into heat, which means you never get 100\% of your work back out.
Teacher's Tip: Heat is the "waste product" of every real-world machine.
Exam Tip: Always use the word "friction" as the primary reason for energy loss.

Question 3: The front end of a boat is shaped like a wedge.
Answer: The front end of a boat is shaped like a wedge so that it can easily cut across the flowing water.
A wedge-shaped bow pushes the water sideways rather than trying to push the whole lake forward. This reduced resistance allows the boat to travel faster and use much less fuel.
Teacher's Tip: Sharp things cut through water easier than flat things!
Exam Tip: Mention that the wedge "splits" the medium (water) to reduce drag.

G Solve the following numerical problems.

Question 1: The length of a lever is 2 m. Calculate its mechanical advantage if the fulcrum is situated at a distance of 40 cm from the effort.
Answer: Length of the lever 2 m = 200 cm. Length of the effort arm 40 cm. Length of the load arm 200 cm - 40 cm = 160 cm. Mechanical advantage ? We know that, Mechanical advantage = Length of effort arm / Length of load arm = 40 cm / 160 cm = 0.25.
Because the effort arm is much shorter than the load arm, the MA is less than 1. This lever would be a speed multiplier, not a force multiplier.
Teacher's Tip: Make sure both lengths are in the same unit (cm) before you divide!
Exam Tip: If MA is less than 1, you can't lift heavy things, but you can move small things very fast.

Question 2: The length of the load arm of a lever is 6 m long and the effort arm is 3 m long. What is the effort required to lift a load of 40 N ?
Answer: Length of the load arm = 6 m. Length of the effort arm = 3 m. Load = 40 N. Effort = ?
We know that Load/Effort = Effort arm/Load arm. By putting values,
we get 40 N/Effort = 3 m/6 m.
Effort = 40 x 6/3 = 80 N.
Since the load arm is twice as long as the effort arm, you actually need twice as much effort as the weight of the load. This lever is used to move a load a long distance with a small push.
Teacher's Tip: Use the "cross-multiplication" trick to solve for the missing number.
Exam Tip: Double-check your final answer; if the load arm is longer, the effort MUST be higher than the load.

Question 3: Calculate the mechanical advantage of a crowbar of length 240 cm if its fulcrum is situated at a distance of 40 cm from the load.
Answer: Length of crowbar = 240 cm. Length of load arm = 40 cm. Length of effort arm = 240 cm - 40 cm = 200 cm. Mechanical advantage = Effort arm / Load arm = 200 cm / 40 cm = 5.
A crowbar is a powerful force multiplier. An MA of 5 means you can lift something five times heavier than the strength you are putting in.
Teacher's Tip: Crowbars are designed for heavy lifting, so they should always have a high MA.
Exam Tip: Remember that the lever length is the SUM of both arms in a Class I lever.

Question 4: What effort will be required to lift a load of 500 N by a single movable pulley ? [Hint: Mechanical advantage of a single movable pulley is two].
Answer: Load = 500 N. Mechanical advantage (MA) = 2 of a single movable pulley. Effort = ? We know that, MA = Load / Effort.
Effort = 500 N / 2 = 250 N.
A movable pulley is a great force multiplier because it cuts the required effort in half. For every 500 N of weight, you only need to pull with 250 N of force.
Teacher's Tip: Movable Pulley = Half the Work!
Exam Tip: Use the provided "hint" directly in your formula for a quick solution.