Maharashtra Board Class 6 Science Chapter 11 Work and Energy Solutions

Std 6 Science Chapter 11 Work And Energy Question Answer Maharashtra Board

Class 6 Science Chapter 11 Work And Energy Question Answer Maharashtra Board

1. Fill in each blank with the appropriate term from the brackets.

Question a.A bucketful of water is to be drawn from a well ............ will be done when a ............ is applied to do this, because there will be an ............ of water. (displacement, workforce)
Answer:work, force, displacement
In simple words: Drawing water from a well involves performing 'work' by applying 'force', leading to the 'displacement' of the water bucket.

🎯 Exam Tip: Remember to choose terms that logically fit the action of work, force, and displacement in physical tasks.

Question b.If a ball is dropped on the sloping roof of a house, it acquires ............ and falls on the ground. That is transformation of ............ energy into ........... energy takes place. (kinetic, potential, motion)
Answer:motion, kinetic, potential
In simple words: A dropped ball first has potential energy, then gains kinetic energy as it moves, converting its potential energy into motion (kinetic energy) as it falls.

🎯 Exam Tip: Understand the conversion between potential and kinetic energy as objects fall or move.

Question c.You might have seen some beautiful fireworks during Diwali. It is an example of transformation of ....... energy into ............ energy. (light, atom, chemical, solar)
Answer:chemical, light
In simple words: Fireworks use stored chemical energy that transforms into light and sound energy when ignited, creating a spectacular display.

🎯 Exam Tip: Chemical energy is often stored in substances and released as other forms of energy through reactions.

Question d.The solar cooker is an application of the ............. energy of the sun, while solar cells, solar lamps are applications of the .............. energy of the sun. (light, chemical, heat)
Answer:heat, light
In simple words: Solar cookers utilize the sun's heat energy to cook food, whereas solar cells and lamps convert the sun's light energy into electricity or illumination.

🎯 Exam Tip: Differentiate between devices that use solar heat and those that use solar light for their function.

Question e.One labourer carried four pans of road metal through a distance of 100 metres. If he carries two pans of road metal through a 200 metre distance ............. work will be done. (equal, more, less)
Answer:equal
In simple words: Work done depends on force and displacement. Carrying half the load for double the distance can result in the same amount of work, assuming the force applied is proportional to the load.

🎯 Exam Tip: Work (W) is calculated as Force (F) × Displacement (d). If force is halved (two pans vs. four) and displacement is doubled (200m vs. 100m), the total work done remains equal (W = F/2 * 2d = Fd).

Question f.The capacity that an object has for doing work is called ............. . (energy, displacement, force)
Answer:energy
In simple words: Energy is defined as the ability or capacity of a system to perform work.

🎯 Exam Tip: Remember the fundamental definition: Energy is the capacity to do work.

2. Match the pairs.

Question a.

Column 'A'	Column 'B'
1. Rolling object	a. Heat energy
2. Food	b. Atomic energy
3. Stretched bow	c. Kinetic energy
4. Sunlight	d. Potential energy
5. Uranium	e. Chemical energy

Answer:

Column 'A'	Column 'B'
1. Rolling object	c. Kinetic energy
2. Food	e. Chemical energy
3. Stretched bow	d. Potential energy
4. Sunlight	a. Heat energy
5. Uranium	b. Atomic energy

In simple words: This matching exercise connects various objects or sources to their primary form of energy, illustrating different types of energy like kinetic, chemical, potential, heat, and atomic.

🎯 Exam Tip: Understand the primary energy form associated with common objects and phenomena to match them correctly.

3. Can you tell?

Question a.When can we say that displacement has taken place?
Answer:When the position of an object changes, we say that the object is displaced.
In simple words: Displacement occurs when an object moves from its initial position to a different final position.

🎯 Exam Tip: Displacement implies a change in an object's location, measured as a vector from start to end points.

Question b.What are the various forms of energy?
Answer:Various forms of energy are: mechanical energy, heat energy, light energy, sound energy, chemical energy and electrical energy.
In simple words: Energy exists in many forms, including the energy of motion, heat, light, sound, chemical bonds, and electric currents.

🎯 Exam Tip: Be able to list and briefly describe the common forms of energy as they are fundamental concepts.

Question c.Describe the natural chain of transformation of energy.
Answer:1. In the course of water cycle, water evaporates due to the heat of the sun. 2. This water vapour forms clouds that give rain. 3. Rainwater flows into rivers and is stored in reservoirs or dams. 4. This stored water at a height has potential energy. 5. As the water falls down, this is transformed into kinetic energy. 6. When the water falls on the turbine, its kinetic energy is transferred to turbine. 7. The turbine rotates producing electrical energy.
In simple words: The water cycle demonstrates natural energy transformation: solar heat causes evaporation, water vapor condenses into clouds (potential energy), which then falls as rain, collecting in dams (potential energy) and flowing through rivers (kinetic energy) to generate electricity (electrical energy).

🎯 Exam Tip: Focus on linking each stage of the water cycle to a specific form of energy transformation, starting with solar energy.

Question d.What should be taken into account for measuring work?
Answer:For measuring work both force and displacement must be taken into account.
In simple words: To calculate work, you need to know both the force applied to an object and the distance it moved in the direction of that force.

🎯 Exam Tip: Work is precisely defined as the product of force and displacement in the direction of the force (W=F×d).

Question e.Why should we save energy?
Answer:Due to increasing population and increasing use of energy resources, there is a danger that limited reserves of coal, petrol, etc. will get exhausted. Hence, we should save energy for future generation.
In simple words: We must conserve energy because conventional resources like coal and petrol are limited and will run out, ensuring enough for future generations.

🎯 Exam Tip: Emphasize the finite nature of fossil fuels and the importance of sustainability for future resource availability.

Question f.What is 'green energy'?
Answer:The energy resources which do not produce smoke and carbon gases such as carbon dioxide or carbon monoxide are called 'green energy resources'. Energy from them is called green energy.
In simple words: Green energy refers to renewable energy sources that do not pollute the environment by releasing harmful gases or smoke.

🎯 Exam Tip: Focus on the environmental benefit and lack of harmful emissions as key identifiers for 'green energy'.

Question g.What are the non-conventional energy resources?
Answer:The resources that: 1. have not been used traditionally. 2. are inexhaustible and continuous. 3. That can be used in various forms again and again are called non-conventional energy resources. 4. e.g.: solar energy, wind energy, tidal energy, hydal power.
In simple words: Non-conventional energy resources are sustainable, continuously available sources like solar, wind, and tidal power, which are newer alternatives to traditional fuels.

🎯 Exam Tip: List key characteristics such as novelty, inexhaustibility, and renewability when defining non-conventional energy sources.

Question h.Which forms of energy from the sun is used in solar energy devices?
Answer:1. Heat energy from the sun is used in solar cookers, solar water heaters, solar driers. 2. Light energy from the sun is used in solar cells, solar panels. 3. Solar electric plants have the capacity to produce electricity on large scale.
In simple words: Solar devices harness the sun's energy in two main forms: heat for applications like cooking and water heating, and light for generating electricity through solar cells.

🎯 Exam Tip: Distinguish between the utilization of solar heat energy (thermal applications) and solar light energy (photovoltaic applications).

Question i.Why should we maximize the use of non- ntional energy sources?
Answer:1. Due to increase in population there is increasing use of conventional sources like petrol, coal, etc. Their reserves are limited and they may get exhausted. 2. Hence, it will be better to use non- conventional sources of energy to save conventional resources for future.
In simple words: Maximizing non-conventional energy sources is crucial to combat the depletion of finite traditional resources and ensure energy availability for future generations.

🎯 Exam Tip: Connect the increased usage of non-conventional sources to the conservation of limited conventional fuels and future sustainability.

4. Who is the odd-one-out?

Class 6 Science Chapter 11 Work And Energy Question 1.Diesel, crude oil, natural gas, wind.
Answer:wind
In simple words: Wind is a renewable energy source, unlike diesel, crude oil, and natural gas which are non-renewable fossil fuels.

🎯 Exam Tip: Classify energy sources as renewable or non-renewable to identify the odd one out.

Work And Energy Class 6 Maharashtra Board Question 2.A running car, hauling a log, a book kept on a table, picking up the school bag.
Answer:A book kept on table.
In simple words: A book kept on a table represents a state of rest with no work being done against gravity or motion, whereas the other options involve movement and work.

🎯 Exam Tip: Work requires both force and displacement; objects at rest are not performing work, though they may possess potential energy.

Work And Energy Class 6 Question 3.Sunlight, wind, wave, petrol.
Answer:Petrol.
In simple words: Petrol is a fossil fuel and a non-renewable energy source, while sunlight, wind, and waves are all renewable and natural energy sources.

🎯 Exam Tip: Differentiate between fossil fuels (non-renewable) and natural, constantly replenishing sources (renewable).

11 Work And Energy Class 6 Question 4.Leaving the fan on in a vacant room, leaving the TV on while working, using A.C during winter, putting off the light when going out.
Answer:putting off the light when going out.
In simple words: "Putting off the light when going out" is the only action listed that represents energy conservation, unlike the others which are examples of energy wastage.

🎯 Exam Tip: Identify actions that promote energy efficiency and conservation versus those that lead to unnecessary energy consumption.

5. Find out the types of energy from the following puzzle.

Question a.Find out the types of energy from the following puzzle.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह एक वर्ग पहेली (word puzzle) है जिसमें अक्षरों का एक ग्रिड दिखाया गया है। इस पहेली में विभिन्न प्रकार की ऊर्जा के नाम छिपे हुए हैं, जिन्हें छात्रों को पहचानना और ढूंढना है।

Z	S	Q	P	Y	M	W	N	E
P	O	T	E	N	T	I	A	L
L	L	S	U	H	V	N	X	I
T	A	O	J	E	V	D	Z	G
Q	R	U	L	A	B	A	D	H
K	I	N	E	T	I	C	Q	T
R	W	D	H	K	L	W	Y	F

Answer:Potential, Kinetic, Solar, Wind, Sound, Light, Heat
In simple words: The puzzle contains various forms of energy such as potential, kinetic, solar, wind, sound, light, and heat, hidden within the grid of letters.

🎯 Exam Tip: Systematically scan the grid horizontally, vertically, and diagonally to identify the hidden energy types.

Work And Energy Exercise Class 6 Question 1.How can you save energy at home and in school? Discuss this with your friends and list all such measures. Put them into practice.

Work And Energy Class 6 Questions Answers Question 2.Find out about energy saving devices available in the market.

Class 6 Science Chapter 11 Work and Energy Important Questions and Answers

Fill in the blanks with suitable words.

Work And Energy Class 6 Exercise Question 1.Falling water possesses ............ energy. (potential, kinetic, chemical)
Answer:kinetic
In simple words: Falling water possesses kinetic energy because it is in motion.

🎯 Exam Tip: Remember that kinetic energy is associated with motion, while potential energy is associated with position or state.

Work And Energy Class 6 Questions And Answers Question 2.Heat is measured in unit called ............ . (kilometres, kilogram, calorie)
Answer:calorie
In simple words: Heat is measured in calories, which is a unit representing the amount of energy required to raise the temperature of water.

🎯 Exam Tip: Know the standard units for different physical quantities; calorie is a common unit for heat energy.

Class 6 Science Chapter 11 Question 3.Plant stores the food in the form of ............ energy. (mechanical, light, chemical)
Answer:chemical
In simple words: Plants convert light energy into chemical energy through photosynthesis, storing it in the form of food.

🎯 Exam Tip: Understand that energy in food and fuels is primarily stored as chemical energy.

11. Work And Energy Class 6 Question 4.We should use ............ energy resources with care. (conventional, non-conventional, both)
Answer:conventional
In simple words: Conventional energy resources like fossil fuels are finite and should be used responsibly to prevent their depletion.

🎯 Exam Tip: Prioritize the careful use of conventional (non-renewable) energy sources due to their limited supply.

Match the columns:

Question 1.

Column 'A'	Column 'B'
1. Solar energy	a. Waves
2. Tidal energy	b. Home cooking
3. Natural gas	c. Car
4. Petrol	d. Solar water heater

Answer:

Column 'A'	Column 'B'
1. Solar energy	d. Solar water heater
2. Tidal energy	a. Waves
3. Natural gas	b. Home cooking
4. Petrol	c. Car

In simple words: This match-the-column exercise pairs various energy sources with their common applications or associated phenomena.

🎯 Exam Tip: Relate each energy source to its primary use or characteristic process to ensure correct matching.

Can you tell?

6th Science Work And Energy Question 1.Water in dams or reservoirs shows potential energy.
Answer:Rainwater flows into river and is stored in reservoirs on dams. These are at height and therefore, their water has potential energy.
In simple words: Water stored at a height in dams and reservoirs possesses potential energy due to its elevated position, which can be converted to other forms of energy.

🎯 Exam Tip: Understand that potential energy is stored energy due to an object's position or state, like water held at a height.

Class 6 Science Chapter 11 Question Answer Question 2.The sun is the most important source of all energy.
Answer:All forms of energy are utilizing indirectly solar energy in all transformation of energy. Therefore, the sun is the most important source of all energy.
In simple words: The sun is the primary energy source because most energy forms on Earth, from fossil fuels to wind and hydropower, originate directly or indirectly from its energy.

🎯 Exam Tip: Recognize the sun's foundational role as the ultimate origin for nearly all energy forms on our planet.

Question 3.What is tidal energy?
Answer:A wall is constructed at a narrow region of a creek. Due to waves generated by high and low tides, the turbine of the generator fitted in the wall starts rotating and electricity is generated.
In simple words: Tidal energy is electricity produced by harnessing the kinetic energy of ocean tides, using barrages or turbines to capture the movement of rising and falling water.

🎯 Exam Tip: Focus on the use of tidal movement (high and low tides) and turbines to convert water's energy into electricity.

Use your brain power!

Question 1.Why do you get hungry after physical exercise?
Answer:1. When we do physical exercise we use the energy stored in the body. 2. To replenish this energy, we have to eat. Hence we feel hungry.
In simple words: Physical exercise consumes the energy stored in our body, triggering hunger as a signal to replenish those energy reserves through food.

🎯 Exam Tip: Connect the expenditure of stored chemical energy during exercise to the body's need for replenishment, leading to hunger.

Question 2.From where does our body get energy.
Answer:Our body gets energy from the food we eat.
In simple words: Our bodies obtain the necessary energy for all functions by breaking down the food we consume.

🎯 Exam Tip: Remember that food is the primary source of chemical energy for the human body.

Question 3.Why do we get tired?
Answer:When we do any work, we use the energy. If this energy level becomes very low, then we feel tired.
In simple words: We feel tired because our body expends its stored energy while performing work, and a significant drop in these energy levels leads to fatigue.

🎯 Exam Tip: Understand tiredness as a physiological response to depleted energy reserves after sustained activity.

Question 4.What is the unit of work and energy?
Answer:The unit of work and energy in SI (System International) is 'Joule'.
In simple words: In the international system of units, both work and energy are measured in Joules.

🎯 Exam Tip: Joule (J) is the standard SI unit for both work and energy, highlighting their close relationship.

Question 5.If no displacement occurs on applying a force, what does it indicate?
Answer:If no displacement occurs, then no work is said to be performed.
In simple words: If an object doesn't move despite a force being applied, it means no work has been done on the object in the scientific sense.

🎯 Exam Tip: Always remember that for work to be done, there must be both force and displacement in the direction of the force.

Can you tell?

Question 1.In the game of marbles, from where does one marble get energy to set another marble in motion?
Answer:When we apply physical force to the fast marble, it gains some force and when it strikes the second marble, energy in the form of force is transferred to the second marble and this force sets the second marble in motion.
In simple words: In marbles, the energy for a stationary marble to move comes from the kinetic energy transferred to it by a moving marble during a collision.

🎯 Exam Tip: This illustrates the principle of energy transfer through collision, where kinetic energy moves from one object to another.

Question 2.While playing carrom from where does the striker gets the energy to make the pieces move?
Answer:When we strike the striker, the force exerted by our muscles is transferred to the striker. When the striker strikes the coin, this energy is transferred to the coin which may help to pocket the coin.
In simple words: The striker gets its energy from the muscular force applied by the player's hand, which is then transferred as kinetic energy to the carrom pieces upon impact.

🎯 Exam Tip: Understand that muscular energy converts to kinetic energy of the striker, which then transfers to the carrom coins upon impact.

Question 3.What will happen as result of the action in the picture?
ℹ️ चित्र व्याख्या (Diagram Explanation): इस चित्र में एक लड़का गुलेल का उपयोग कर रहा है। लड़का गुलेल के रबर बैंड को खींचकर पत्थर को फेंकने की तैयारी कर रहा है, जो स्थितिज ऊर्जा के संचयन को दर्शाता है।

Question i.The rubber band is released after streaching it.
Answer:It comes back to its orriginal position.
In simple words: When a stretched rubber band is released, the stored potential energy causes it to snap back to its original, unstretched shape.

🎯 Exam Tip: Elastic potential energy stored in a stretched object converts back to other forms (like kinetic) as it returns to its resting state.

Question ii.A stone is held in the rubber of a catapult, the rubber is stretched and released.
Answer:Stone gets thrown to a distance and rubber band cones back to its original position.
In simple words: When a stretched catapult's rubber is released, its stored potential energy is transferred to the stone, propelling it forward, while the rubber returns to its relaxed state.

🎯 Exam Tip: This demonstrates the conversion of potential energy stored in the stretched rubber into kinetic energy of the stone.

Let's try this.

Question 1.If we hold a convex lens over a sheet of paper in sunlight such that there is tiny spot of light on the paper for a while. What happens? Why?
Answer:1. If a convex lens is held over a paper in sunlight such that there is a tiny spot of light on the paper for a while the paper bums. 2. This is due to the heat energy of the sun concentrated at a point due to the convex lens.
In simple words: A convex lens focuses sunlight into a small, intense spot, concentrating the sun's heat energy sufficiently to burn the paper.

🎯 Exam Tip: Convex lenses converge light rays, and when used with sunlight, they can concentrate solar energy (both light and heat) to a focal point.

Question 2.How does a picture appear on the screen of a TV?
Answer:When a TV is switched on, the electrical energy is converted into light and sound energy. Hence, a picture appears on TV.
In simple words: When a TV is turned on, it converts electrical energy into light energy for the picture and sound energy for audio, allowing us to see images and hear sounds.

🎯 Exam Tip: Understand that electronic devices like a TV convert electrical energy into multiple forms, primarily light and sound, to function.

Question 3.In which form is energy stored in plant food?
Answer:Energy stored in plant food is in the form of chemical energy.
In simple words: Plant food contains energy stored in its chemical bonds, which is known as chemical energy.

🎯 Exam Tip: Remember that energy in organic matter like plant food is always stored as chemical energy.

Question 4.How is energy obtained from cooking gas?
Answer:Energy obtained from cooking gas is heat energy which is obtained by conversion of chemical energy.
In simple words: Cooking gas stores chemical energy, which is released as heat energy when burned, making it useful for cooking.

🎯 Exam Tip: Recognize that combustion (burning) processes convert chemical energy stored in fuels into heat energy.

Question 5.Why is Energy not visible to us?
Answer:Energy is the capacity to do work. Energy is converted from one form to another in the form of work being done. Hence it is not visible to us.
In simple words: Energy is not a physical substance but a concept representing the capacity to do work; we observe its effects as transformations, not its direct form.

🎯 Exam Tip: Energy is an abstract physical quantity, often perceived through its manifestations (like light, heat, motion) rather than as a visible entity itself.

How are we different from each other?

Question 1.Potential energy and Kinetic energy
Answer:

Potential energy	Kinetic energy
1. Energy stored in an object due to its position is called potential energy.	1. Energy possessed by a body due to its motion is called kinetic energy.
2. No work is performed.	2. Work is performed.

In simple words: Potential energy is stored energy based on an object's position or state, while kinetic energy is the energy of an object due to its motion.

🎯 Exam Tip: Differentiate between potential energy (stored, positional) and kinetic energy (moving, active) based on their definitions and effects.

Question 2.Work and energy
Answer:

Work	Energy
1. When an object is displaced by applying force on it, work is said to be done.	1. Energy is the capacity to do work.
2. Work is done as a result of using energy.	2. Energy is the cause for work to be done.

In simple words: Energy is the capacity to perform work, whereas work is the actual process of transferring energy by a force causing displacement.

🎯 Exam Tip: Understand that energy is a prerequisite for work, and work is the manifestation of energy transfer or conversion.

Question 3.Conventional and Non-conventional energy sources
Answer:

Conventional source of energy	Non-Conventional source of energy
1. Man has been using these energy resources for centuries.	1. These resources have not been used traditionally.

In simple words: Conventional energy sources are traditional, often finite resources used for centuries, while non-conventional sources are newer, typically renewable, and sustainable alternatives.

🎯 Exam Tip: Distinguish between conventional (historical, often finite) and non-conventional (modern, renewable) energy sources based on usage and availability.

Classify as directed:

Question 1.Into kinetic and potential energy Waterfalls, water in a reservoir, a stretched spring, a boy running in a race.
Answer:
- Potential - water in a reservoir, a stretched spring.
- Kinetic - waterfalls, a boy running in a race.
In simple words: Water in a reservoir and a stretched spring possess potential energy due to their position or state, while waterfalls and a running boy exhibit kinetic energy because of their motion.

🎯 Exam Tip: Identify potential energy with stored energy (due to height, compression/stretching) and kinetic energy with energy of motion.

Define:

Question 1. Work
Answer: When an object is displaced by applying a force on it, work is said to be done.
In simple words: Work happens when a force causes an object to move a certain distance. If there's no movement, no work is done.

🎯 Exam Tip: Understanding the basic definition of work (force multiplied by displacement in the direction of force) is crucial for foundation concepts.

Question 2. Energy
Answer: Energy is the capacity to do work.
In simple words: Energy is simply the ability to perform work or cause change. Without energy, nothing can move or transform.

🎯 Exam Tip: Define energy clearly, emphasizing its role as the capacity for work. This is a fundamental concept in physics.

Question 3. Chemical energy
Answer: The energy obtained through chemical action is called chemical energy.
In simple words: Chemical energy is stored in the bonds of molecules and is released during chemical reactions, like when we burn fuel or digest food.

🎯 Exam Tip: Relate chemical energy to everyday examples like fuels or food, and mention its release during chemical transformations.

Question 4. Potential energy
Answer: The energy which is stored in an object due to a specific state or position of that object is called potential energy.
In simple words: Potential energy is stored energy an object has because of its position or state, ready to be converted into other forms of energy.

🎯 Exam Tip: Differentiate potential energy from kinetic energy by emphasizing its 'stored' nature due to position (e.g., height) or configuration (e.g., stretched spring).

Question 5. Kinetic energy
Answer: The energy obtained by the virtue of its motion is called kinetic energy.
In simple words: Kinetic energy is the energy an object possesses because it is moving. The faster or heavier an object is, the more kinetic energy it has.

🎯 Exam Tip: Focus on the keyword 'motion' when defining kinetic energy. Provide simple examples like a rolling ball to illustrate the concept.

Question 6. Solar energy
Answer: The enormous and continuous energy obtained from the sun is called solar energy. Solar energy is at the root of all energy available on earth.
In simple words: Solar energy is the vast, continuous energy coming from the sun, which is the primary source for almost all other energy forms on Earth.

🎯 Exam Tip: Highlight solar energy's status as a primary, continuous, and enormous energy source, fundamental to nearly all life and energy systems on Earth.

Question 7. Conventional energy resources: (non-renewable energy sources)
Answer: The energy sources which man has been using for centuries and that cannot be replenished are called conventional energy sources.
In simple words: Conventional energy resources are traditional energy sources, like coal and oil, that have been used for a long time and cannot be replaced once they are used up.

🎯 Exam Tip: For conventional energy, emphasize their long history of use and, crucially, their non-renewable nature. Provide examples like fossil fuels.

Question 8. Renewable energy sources: (non-conventional energy sources)
Answer: The resources that have not been used traditionally and that are inexhaustible, continuous and can be used in various forms again and again are called renewable energy sources.
In simple words: Renewable energy sources are new, continuous, and inexhaustible resources like solar or wind power that can be used repeatedly without running out.

🎯 Exam Tip: When discussing renewable energy, focus on their inexhaustible and continuous nature, distinguishing them from conventional sources. Give examples like solar and wind.

Explain - why?

Question 1. Energy is not visible to us.
Answer: There is energy in every substance in the universe. It is present in non-living as well as living things. But still we can only feel the energy when some work is done, e.g. When wind blows, we can feel the coolness in air. When we switch on the light in a dark room, we can see things due to light energy.
In simple words: Energy isn't visible because it's an abstract capacity to do work, not a physical object. We perceive its effects when it causes changes or work to be done, like feeling wind or seeing light.

🎯 Exam Tip: Explain that energy is an abstract concept, observable only through its effects (work, changes), not as a visible substance.

Question 2. Save energy, (use alternative energy sources)
Answer:
(i) Due to increasing population, there is increasing usage of energy resources.
(ii) There is a danger that limited reserves of conventional resources like diesel, crude oil, may get exhausted.
(iii) We should save energy so that future availability is ensured.
(iv) It will be better to use alternative and supplementary energy sources.
In simple words: We must save energy and use alternative sources because our population is growing, conventional resources are limited and depleting, and ensuring energy for future generations is crucial.

🎯 Exam Tip: Emphasize the sustainability aspect—saving energy and using alternatives ensures resource availability for future generations and reduces environmental impact.

Question 3. Methods of saving energy.
Answer:
(i) Saving energy is as good as generating energy.
(ii) There are several ways of saving energy such as putting off lamps when not needed.
(iii) Making maximum use of sunlight.
(iv) Saving energy and energy resources is absolutely necessary. Otherwise, we will have to face the serious calamity like global warming.
In simple words: Saving energy is like creating it; methods include turning off lights, maximizing sunlight use, and it's essential to prevent global warming and resource depletion.

🎯 Exam Tip: Focus on practical, everyday methods of energy conservation and connect it to broader environmental concerns like global warming.

Question 4. State the energy conversions in following cases.
Answer:
(i) Solar water heater - Solar energy to heat energy
(ii) Solar cell - Solar energy to electrical energy
(iii) Fission of uranium, thorium - Atomic energy to heat energy and then to electrical energy
(iv) Switch on mixer - Electrical energy to mechanical energy
(v) Switch on lamp - Electrical energy to light energy
(vi) Switch on TV - Electrical energy to light energy and sound energy
(vii) Switch on radio - Electrical energy to sound energy,
(viii) Ram plays tabla - Mechanical energy to sound energy
(ix) Ravi plays shehnai - Wind energy to sound energy
(x) You switch on the torch - Chemical energy to light energy
(xi) Your mother lights the gas stove to cook - Chemical energy to heat energy
(xii) Dinesh is bursting crackers during Diwali - Chemical energy to heat, light and sound energy
In simple words: This question demonstrates how energy changes forms in various scenarios, from solar to electrical, chemical to heat, and electrical to mechanical, light, or sound.

🎯 Exam Tip: Practice identifying the initial and final forms of energy in various common activities. Understanding energy transformation is key to this chapter.

ℹ️ चित्र व्याख्या (Diagram Explanation): इस चित्र में एक लड़की दो अलग-अलग बक्सों को खींच रही है। पहले चित्र में एक हल्का या खाली बक्सा है, जबकि दूसरे चित्र में एक भारी बक्सा (संभवतः किताबों से भरा हुआ) है।

Question i. In the above activity, which are the different forces acting on the box?
Answer: In the above activity, muscular force, frictional force and gravitational force act on the box.
In simple words: When pulling the box, the girl applies muscular force, friction resists the movement, and gravity pulls the box downwards.

🎯 Exam Tip: Remember to consider all relevant forces: applied force (muscular), resistive force (friction), and natural forces (gravity).

Question ii. Is displacement possible without force?
Answer: No, force has to be applied in order to displace the box.
In simple words: No, displacement is not possible without an applied force; an object needs a push or pull to change its position.

🎯 Exam Tip: Understand Newton's first law—an object at rest stays at rest unless acted upon by an external force.

Question iii. If force is applied to both the boxes is same, which box will be displaced more?
Answer: If force applied to both the boxes is same, then empty box will be displaced more than box with books.
In simple words: If the same force is applied, the lighter empty box will move a greater distance than the heavier box filled with books because it has less inertia.

🎯 Exam Tip: Recall that for a constant force, an object with less mass (lighter) will experience greater acceleration and thus greater displacement over the same duration compared to a heavier object.

Question iv. If me e books are added to box, and same force is applied, will the displacement be more or less?
Answer: If the same force is applied for a heavier load then the displacement will be less.
In simple words: If more books are added, increasing the load, the displacement will be less for the same amount of applied force due to increased mass.

🎯 Exam Tip: Remember that increasing the mass of an object (making it heavier) will result in less displacement if the applied force remains constant.

Question v.a. If a force is applied with both the hands on a wall, will there be a displacement?
Answer: Whatever be the amount of force applied, the wall will not be displaced.
In simple words: No, the wall will not be displaced because it is too heavy and fixed, meaning your applied force isn't enough to overcome its inertia and the forces holding it in place.

🎯 Exam Tip: Displacement requires the applied force to be greater than any opposing forces and the object's resistance to change in motion.

Question b. If no displacement occurs on applying as force, what does it indicate?
Answer: If no displacement occurs, then no work is said to be performed.
In simple words: If an object doesn't move despite a force being applied, it means no work has been done on the object, even if effort was expended.

🎯 Exam Tip: Reiterate the definition of work: force multiplied by displacement. If displacement is zero, work is zero.