# CBSE Class 9 Physics Work And Energy Worksheet Set A

Read and download free pdf of CBSE Class 9 Physics Work And Energy Worksheet Set A. Students and teachers of Class 9 Physics can get free printable Worksheets for Class 9 Physics in PDF format prepared as per the latest syllabus and examination pattern in your schools. Standard 9 students should practice questions and answers given here for Physics in Grade 9 which will help them to improve your knowledge of all important chapters and its topics. Students should also download free pdf of Class 9 Physics Worksheets prepared by school teachers as per the latest NCERT, CBSE, KVS books and syllabus issued this academic year and solve important problems provided here with solutions on daily basis to get more score in school exams and tests

## Work And Energy Class 9 Physics Worksheet Pdf

Class 9 Physics 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 Physics will be very useful for exams and help you to score good marks

### Class 9 Physics Worksheet for Work And Energy

CBSE Class 9 Physics Worksheet - Work & Energy

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Work & Energy (Physics)

1. Under what conditions work is said to be done?

2. Derive the formula for work done by a constant force

3. Give few examples where energy is possessed by a body due to its change in shape.

4. State and prove the law of conservation of energy.

5. Is it possible that force is acting on a body but still work done is zero? Explain.

6. A rocket of mass3x106 kg takes off from a launching pad and acquires a vertical velocity of 1km/s at an altitude of 25 km. calculate (a) the potential energy and (b) the kinetic energy. (g = 9.8m/s2)

7. If a man lifts a load up with the help of a rope such that it raises the load of mass 50kg to a height of 20m in 100 sec. Find the power of man

8. A ball is dropped from a height of 5m. Find the velocity of the ball just before it reaches the ground. Do you require the value of mass to find the velocity?

9. Two persons A and B do same amount of work. The person A does that work in t1sec and the person b in t2sec. Find the ratio of power delivered by them.

10. Why do our hands become warm when rubbed against each other? Explain.

11. The kinetic energy of a body of mass 15 kg is 30j. What is its momentum?

12. Give an example for each of the following energy conversion: (1) electrical energy to kinetic energy. (2) Chemical energy to electrical energy (3) sound energy to electrical energy

13. Two bodies have same momentum. Which will have greater kinetic energy- heavier body or lighter body?

14. An electric bulb of 60w is used for 6h per day .Calculate the units of energy consumed in one day by the bulb.

15. A boy of mass 50kg runs up to a stair case of 45 steps in 9s. If the height of a step is 15cm, find his power. (g= 10m/s2)

16. Two particles of masses 1g and 2g have equal momentum. Find the ratio between their kinetic energies?

17. What will be the work done by the string, when a stone is tied to a string and whirled in a circle?

18. A locomotive exerts a force of 7500N and pulls a train through 1.5 km. How much work is done by locomotive?

19. What work a boy of mass 50kg will do in order to increase running speed from 9km/h to 18km/h.

20. The speed of a moving body is halved. What is the change in its K.E.?

21. State the energy changes taking place in the following cases: (1) A car moves up a hilly road.(2) a stone projected vertically upward returns

22.When we cut a log of wood with a saw it becomes warm, why?

Exam Questions NCERT Class 9 Science Chapter 11 work And Energy

Question. A light and a heavy body have equal kinetic energy. Which one is moving fast?
Ans : The lighter body is moving fast.

Question. State the relation between kWh and joule. Define 1 watt.
Ans : 1 kWh – 1000 Wh = 1000 Js–1 × 60 × 60 s
= 3.6 × 106 J
1 watt is the power of an agent which can do one joule of work in one second.

Question. Can kinetic energy of a body be negative?
Ans : No as mass and velocity cannot be negative

Question. What is the energy of a body due to its motion called?
Ans :Kinetic energy.

Question. What is the SI unit of kinetic energy?
Ans : Joule.

Question. Can any object have mechanical energy even if its momentum is zero? Explain.
Ans : Yes, mechanical energy comprises of both potential energy and kinetic energy. Zero momentum means that velocity is zero. Hence, there is no kinetic energy but the object may possess potential energy.

Question. Give one example each of potential energy (i) due to position (ii) due to shape.
Ans : (i) Potential energy due to position : Water stored in dam has potential energy.
(ii) Potential energy due to shape : In a toy car, the wound spring possesses potential energy and as the spring is released, its potential energy changes into kinetic energy due to which the car moves.

Question. What kind of energy transformation takes place when a body is dropped from a certain height?
Ans : When a body falls, its potential energy gradually gets converted into kinetic energy. On reaching the ground, the whole of the potential energy of the body gets converted into kinetic energy.

Question. Can energy be destroyed? Can energy be created?
Ans : No, energy can neither be created nor be destroyed.

Question. A cell converts one form of energy into another. Name the two forms.
Ans : It converts chemical energy into electrical energy.

Question. Name one unit of power bigger than watt.
Ans : A unit bigger than watt is kilowatt.

Question. A spring which has been kept compressed by tying its ends together is allowed to be dissolved in an acid. What happens to the potential energy of the spring?
Ans : The PE of the spring gets converted into KE of acid molecules whose temperature rises.

Question. Justify giving proper reasoning whether the work done in the following case is positive or negative – Work done by resistive force of air on a vibrating pendulum

in bringing it to rest.
Ans : Work done is negative because the resistive force of air always acts opposite of the direction of motion of the vibrating pendulum.

Question. The work done in lifting a box on to a platform does not depend upon how fast it is lifted up. Explain your answer giving proper reasoning.

Ans : The work done (W) in lifting a box through a distance
(s) against the gravitational force (F) is given by W =
Fs. Hence, it is obvious that it is independent of the
rate at which the box is lifted.

Question. A body of mass 2 kg is moving with a speed of 20 m/s.
Find the kinetic energy.
Ans : KE = 0.5 mv2
= 0.5 × 2 × 20 × 20 = 400 J

Question. At what rate is electrical energy consumed by a bulb of 60 watt?
Ans : A 60 watt bulb consume electrical energy at the ratio of 60 joule per second.

Question. Which type of energy is present in an atom?

Ans : Nuclear energy.

Question. Define energy.
Ans : Energy is the ability of a body to do work. It is also defined as the capacity to do work.

Question. A body performs no work. Does it imply that the body possesses no energy?
Ans : When a body does not perform any work, it never implies that the body has no energy. The body may have energy but still does not perform any work, e.g., a book placed on a table has potential energy but is not performing any work.

Question. (a) What is meant by potential energy? Is potential energy vector or scalar quantity?
(b) Give one example of a body having potential energy.
Ans : (a) The energy possessed by a body by virtue of its position or configuration. It is a scalar quantity.
(b) Stretched string of a bow.

Question. When is the work done by a force said to be negative?

Give one situation in which one of the forces acting on the object is doing positive work and the other is doing negative work.
Ans : We know that work done W = Fs cos q , where q is the angle between F and S. Clearly, W will be – ve, if q is between 90° and 180° because then cos q will be –ve. Consider the case of a body falling under gravity. The body experiences an upward frictional force and downward force due to gravity. Since, the body is moving downwards, the work done by force
to gravity will be +ve but that is against the upward thrust will be –ve.

Question. A light and a heavy body have the same momentum.
Which one will have greater kinetic energy?
Ans :
As K =p2/2m and p is same for both. Hence, K∝ m/1 Thus, the lighter body has more kinetic energy thanbthe heavier body.

Question. (i) What is a closed system?

(ii) State the law of conservation of energy.
Ans : (i) A system that does not interact with another is a closed system. Energy in a closed system is neither taken out of it nor taken in from outside. However, energy transformation may occur inside a closed system.
(ii) The law of conservation of energy states that “the energy can neither be created nor destroyed, but can be transformed from one form to another. In other words, the total energy of a closed system remains constant. Therefore, whenever one from of energy disappear, an equivalent amount of another form appears.

Question. Is it possible that a body be in accelerated motion under a force acting on the body, yet no work is being done by the force? Explain your answer giving a suitable example.
Ans : Yes, it is possible, when the force is perpendicular to the direction of motion. The Moon revolving round the Earth under the centripetal force of attraction of the Earth, but Earth does no work on the motion.

Question. A body moves along a circular path. How much work is done in doing so? Explain.

Ans : In case of a body moving along a circular path, the force (centripetal) is always along the radius while displacement is tangential. Hence, work done W = FS
cos 90° = 0 as angle between F and S is 90°.

Question. A battery lights a bulb. Describe the energy changes involved in the process.
Ans : Within the electric cell of the battery the chemical energy changes into electrical energy. The electric energy on flowing through the filament of the bulb, first changes into heat energy and then into the light energy.

Question. What kind of energy transformations take place at a thermal power station?

Ans : At a thermal power station, the chemical energy of coal is changed into heat energy which is further changed into electrical energy with the help of an electric generator.

Question. (a) How much work is done when a force of 1 N moves a body through a distance of 1 m in its direction?
(b) Is it possible that a force is acting on a body but still the work done is zero? Explain giving one example.
Ans : (a) 1 J of work is done.
(b) Yes, it is possible when force acts at right angles to the direction of motion of the body. Example :
Gravitational force of Earth acts on a satellite at right angles to its direction of motion.

Question. Is it possible that a body is in accelerated motion tinder a force acting on the body, yet no work is being done by the force? Explain your answer giving a suitable example.

Ans : Yes, it is possible, when the force is perpendicular to the direction of motion. The Moon revolving round the Earth under the centripetal force of attraction of the Earth but Earth does not do any work on the motion of the Moon.

Question. Does the potential energy of a spring increase or decrease when it is compressed?
Ans : The potential energy of the spring increases because work is done on it when it is compressed.

Question. A spring is compressed, what change is expected in the potential energy of the spring

Ans : When a spring is compressed, its potential energy is used up to changing its shape.

Question. A man rowing a boat upstream is at rest with respect to the shore. Is he doing work?
Ans : The man is doing work relative to the stream because he is applying force to produce relative motion between the boat and the stream. But he does zero work relative to the shore as the displacement relative to the shore is zero.

Question. What type of energy is stored in the spring of a watch?

Ans : When we wind a watch, the configuration of its spring is changed. The energy stored in the spring is obviously potential in nature (elastic potential energy to be more accurate).

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