## Work And Energy Class 9 Science Worksheet Pdf

Class 9 Science students should refer to the following printable worksheet in Pdf for Work And Energy in standard 9. This test paper with questions and answers for Grade 9 Science will be very useful for exams and help you to score good marks

### Class 9 Science Worksheet for Work And Energy

CBSE Class 9 Science Worksheet - Work and Energy. Students can download these worksheets and practice them. This will help them to get better marks in examinations. Also refer to other worksheets for the same chapter and other subjects too. Use them for better understanding of the subjects.

**Exam Questions NCERT Class 9 Science Chapter 11 work And Energy**

**Question: In a tug-of-war one team gives way to the other. What work is being done and by whom?****Answer :** The winning team does work. The work is equal to the product of the resultant force and the displacement undergone by the losing team.**Question: What will cause greater change in kinetic energy of a body? Changing its mass or changing its velocity?****Answer :** Changing its velocity.**Question. List two essential conditions for work to be done.****Answer :** (i) A force must act and

(ii) There should be displacement in the body.

**Question: A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force. Let us take it that the force acts on the object through the displacement . What is the work done in this case?****Answer :** Given,

displacement = 8 m,

Force = 7 N

Now, Work done = Force × Displacement

= 7 × 8 = 56 J

**Question: What is the work done by a coolie walking on a horizontal platform with a load on his head?****Answer :** In order to balance the load on his head, the coolie applies a force on it in the upward direction, equal to its weight. His displacement is along the horizontal direction. Thus, the angle between force F and displacement is 90°. Therefore, work done W = Fs cos q = Fs cos 90° = 0.** Question: We wind our watch once a day, what happens to the energy?**

**Answer :**When we wind our watch, we wind the spring inside the watch. As a result, energy is stored in the spring in the form of elastic potential energy. This elastic potential energy is used to make the watch work the whole day.

**Question: Will work be done by a man who pushes a wall?****Answer :** No.

**Question: Name the form of energy associated in each case :****(i) A flying bird.****(ii) A man climbing the stairs.****(iii) A compressed watch spring.****(iv) A fast moving object.****Answer :** (i) Mechanical energy

(ii) Mechanical energy

(iii) Potential energy

(iv) Kinetic energy** Question: Name the various forms of energy.**

**Answer :**The various forms of energy are :

(i) Potential energy

(ii) Kinetic energy

(iii) Mechanical energy

(iv) Heat energy

(v) Chemical energy

(vi) Electrical energy

(vii) Light energy.

**Question: What is the work done when the force acting on the body and the displacement produced in the body are at right angles to each other?**

**Answer :**Zero

**.**

**Question: Write an expression for the work done in lifting a body of mass ‘m’ through a vertical height ‘h’.****Answer :** Work done W = mgh, where g is acceleration due to gravity.

**Question: What is the work done on a body moving in a circular path?****Answer :** Zero, because force and displacement are perpendicular to each other.**Question: When a book is lifted from a table, against which force work is done?****Answer :** Work is done against the force of gravity.

**Question: Distinguish between work, energy and power. State the SI units for each of these quantities.****Answer :**** Work :** It is defined as the product of force applied and the distance moved by the body on the application of the force. In SI unit it is measured in joule.**Energy :** It is defined as the capacity of a body to do work. In SI unit it is measured in joule. **Power :** It is defined as the rate of doing work. It measures how fast or slow the work is done. In SI unit it is measured in watt unit.

**Question: What is the relationship between megawatt and watt?****Answer :** 1 megawatt = 106 watt

**Question: What is the relationship between megawatt and joules per second?****Answer :**** **1 megawatt = 106 joule/second

1 MW = 106 js–1

**Question:Define work. How is work measured? When is work done by a force negative?****Answer :** Work is said to be done if force acting on an object displaces it through a certain distance.

It is measured as the product of force and displacement.

Work done is negative if force and displacement are in the opposite direction.** Question: What is the work done by the force of gravity in the following cases?**

**(a) Satellite moving around the Earth in a circular orbit of radius 35000 km.**

**(b) A stone of mass 250 g is thrown up through a height of 2.5 m.**

**Answer :**

(a) Zero, as the displacement in one complete revolution is zero.

(b) Given m = 250 g = 0.25 kg, h = 2.5 m, g = 10

ms–2, W = ?

Now, W = Fs = mg × h

= 0.25 × 10 × 2.5 = 6.25 J

Question: Define 1 J of work.

Question: Define 1 J of work.

**Answer :**Work done = Force x Displacement Force, F = 1 N and displacement, s = 1 m, then the work done by the force will be 1 Nm or 1 J. Thus, 1 J is the amount of work done on an object when a force of 1 N displaces it by 1 m along the line of action of the force.

**Question: What is the amount of work done by a force when a body moves in a circular path?****Answer :**

Work done is given by the expression W = Fs cos q

. When a body moves in a circular path, then the

displacement (s) is zero. Therefore, work done is

W = F × 0 = 0.

**Question: Name the common forms of the mechanical energy.****Answer :** The common forms of the mechanical energy are :

(i) Kinetic energy

(ii) Potential energy

**Question: Does every change in energy of the body involve work?****Answer :** Yes.

**Question: Is it possible that some force is acting on a body but still the work done is zero?****Answer :** Yes, when force acts at an angle of 90° with the displacement.

**Question: The masses of scooter and bike are in the ratio of 2 : 3 but moving with same speed of 108 km h–1. Compute the ratio of their kinetic energy.****Answer :** The energy possessed by a body by virtue of its motion.

Given, m1/m2=2/3

2 , the ratio of KE is equal to the ratio of their masses if they have the same velocity, therefore,ratio of their KE is also 2 : 3.

**Question: Define power. Write commercial unit and SI unit of electrical energy. An electrical geyser of 1.5 kW works for 2 hours. Find the electrical energy units consumed in a day.****Answer :** Power is defined as the rate of doing work. SI unit s joule and kWh is the commercial unit of electrical energy.

Given, P = 1.5 kW,

t = 2 hours,

E = P × t = 1.5 × 2 = 3 kWh

**Question: A force of 10N causes a displacement of 2 m in a body in its own direction. Calculate the work done by force.****Answer :** The work done by force = F × s = 10 N × 2 m = 20 J

**Question: A body of 5 kg raised to 2 m find the work done.****Answer :** The work done to raise a body

= PE

= mgh

= 5 kg × 9.8 × 2 = 98 joule

**Question: A moving body of 30 kg has 60 J of KE. Calculate the speed.****Answer :**

KE = 0.5 mv2

60 = 0.5 × 30 × v2

60 = 15 v2

v = 2 m/s

**Question: What is meant by the term horsepower (hp)?****Answer :** Horsepower is another commercial unit power

1 hp = 746 W

1W = 746

1 hp = 0.0013 hp

**Question: What is the kinetic energy of an object?****Answer :** The energy possessed by a body by virtue of its motion is called kinetic energy.

**Question: Write an expression for the kinetic energy of an object.****Answer :** The expression is KE = 2

1 mv2 where ‘m’ is the mass

and v is the velocity of the body.

**Question: Define 1 watt of power.****Answer :** When a work of 1 joule is done in 1 s, the power is said to be one watt.

**Question: Define average power.****Answer :** When a machine or person does different amounts of work or uses energy in different intervals of time, the ratio between the total work or energy consumed to the total time is average power.**Question: What is the relationship between horse power and watt?****Answer :** 1 horsepower = 746 watt

1 hp = 746 W

**Question:An electric kettle of 500W is used to heat water everyday for 2 hours. Calculate the number of unit of electrical energy consumed by it in 10 days.****Answer :** E = Pt = 500 W × 10 × 2h

= 10000 Wh

= 10 kWh = 10 unit

**Question:** How does the kinetic energy of a body change if the mass of the body is halved?**Answer:** If the mass of a body is heaved the kinetic energy is also halved.

**Question:** A car and a truck are moving with the same velocity of 60 km/hr–1, which one has more kinetic energy?**Answer :** Truck has more kinetic energy as kinetic energy is directly proportional to the mass.

**Question: By how much will the speed of a body, of fixed mass, increase if its kinetic energy becomes four times its initial kinetic energy?****Answer :** The speed is doubled.

**Question: Can a body possess energy even if it is not in motion?****Answer :** Yes, it can possess potential energy.

**Question: What is the relationship between watt and joules per second.****Answer :** 1 Watt = 1 joule/second

1 W = 1 Js–1

**CONCEPTUAL QUESTIONS**

**Question: **Name the physical quantity having the unit of Newton-metre

**Question: **Under what condition the work done by a force is zero

**Question: **** **ive the relation between momentum and kinetic energy of a body.

**Question: **Give two examples for work done by a force to be negative.

**Question: **When an arrow is shot from its bow, it has kinetic energy. From where does it get this kinetic energy?

**Question: **Can an object have mechanical energy even if its momentum is zero. Also can an object have momentum without energy. Explain.

**Question: **What is Power? Show that power = Force × velocity

**Question: **State the commercial unit of energy and express it in joule.

**Question: **Explain the energy changes taking place in a simple pendulum

**Question: **Why no work is being done for planetary motion?

**Question: **wo bodies of different masses m1 and m2 (m1 > m2 ) are moving with same kinetic energy. Which one does greater work? If they are stopped by applying brakes which body will stop first and why?

**Question: **(a)A truck and car are moving with same velocity. Which of the two would have less kinetic energy?

(b )Give an example of electrical energy converted into light energy.

(c)An electric bulb is rated 15 Watts. Explain the statement.

**Question: **** **Name the energy possessed by the following:

(a) Flying aeroplane

(b)Water stored in the dam

(c) Stretched spring

(d)Blades of a working mixer

**Question: **** **Explain the energy conversion taking place in the following

(a) Nuclear explosion

(b) Photosynthesis

(c) During lightning

**Question: **** **State and prove the law of conservation of energy?

**SECTION-B**

**NUMERICAL PROBLEMS**

**Question: **A boy and a girl are running with the same speed. If the mass of the boy is 20 times that of the girl, find the ratio of their kinetic energy?

**Question: **An electric motor has an output power of 2400 W and is used to raise a ship’s anchor. If the tension in the cable is 8 kN, at what constant speed is the anchor being raised ?

**Question: **Water is falling on the blades of the turbine at a rate of 6x103 kg per minute at a height of 10m. Calculate the power given to the turbine.(Take g =10m/s2 )

**Question: **A body A of mass 3 kg and body B of mass 2 kg are dropped simultaneously from a height of 14.9 m. Calculate the ratio of a) Their momenta b) their kinetic energies

**Question: **Two forces are acting on a body. First force of 5N from west to east and second force of 3N from east to west to displace it to a distance of 5m. What is the work done by the forces and in which direction the displacement takes place.

**Question: **What do you understand by the units of electrical energy? How many joules of energy is consumed if the Watt hour meter shows 400 units of energy?

**Question: **A stone is thrown vertically upwards with a velocity of 40m/s.

(a) At what height will its kinetic energy and potential energy be equal

(b) Calculate the P. E. of the body if its mass = 10Kg

**Question: **A body of mass 5Kg is lifted vertically at a constant velocity of 12m. calculate

(a) the force applied

(b) work done in lifting the body

(c) what happens to the work performed ?

**Question: **A boy having mass of 40kg runs up a flight of 50 steps, each step is 10cm high and the boy crosses each step in 5 seconds. Calculate

(a)Work done

(b)Power developed (given g = 9.8ms-2)

**Question: **An electric kettle of power 500W and a geyser of power 2kW are used 2hours everyday. Calculate the cost of using them for 60 days if the cost is Rs.1.50 per unit?

**Question: <#> Kinetic energy of a moving object is the energy**

(A) Possessed by an object due to its motion

(B) That increases with speed

(C) Equal to the work done on it to make it acquire that velocity.

(D) All of these

**Question: <#> Negative value of work done indicates that**

(A) Force and displacement are in the same direction

(B) More than one force is acting on the object

(C) Displacement and force are in opposite directions

(D) Both (2) and (3

**Question: <#> Unit of work done is**

(A) Joule

(B) Newton meter

(C) Calorie

(D) Both (1) and (2)

**Question: <#> Work done is defined as**

(A) Product of force and displacement

(B) Distance through which the object is moved

(C) Mass of the object getting displaced

(D) Product of force and mass

**Question: <#> Scientific concept of work suggest that work is said to be done if**

(A) A force acts on an object

(B) The object must be displaced

(C) acceleration should be there.

(D) Only (1) and (2)

**Question: <#> 1 kilowatt = -----**

(A) 1000 W

(B) 1000 J s –1

(C) 1000 N m s –1

(D) All of these

**Question: <#> Commercial Unit of power is kilowatt-hour (kW h)**

(A) 1 kW h = 3.6 x 106 J

(B) 1 kWh is the energy consumed in one hour at the rate of 1000 J s –1

(C) 1 kWh = 1 unit of electrical energy

(D) All these statements are correct

**Question: <#> An electrical appliance of 500W is used for 5 hours per day. Energy consumed in 30 days will be**

(A) 2.5 kW h

(B) 25 kW h

(C) 75 kW h

(D) None of these

**Question: <#> What is energy of a body?**

**Question: <#> Define kinetic energy.**

**Question:) <#>What is potential energy?**

**Question: <#>What will be the work done by a force if displacement of the body is zero?**

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