# CBSE Worksheet for chapter-8 Work, Energy & Power class 9

## Find CBSE Worksheet for chapter-8 Work, Energy & Power class 9

CLASS-9

BOARD: CBSE

Physics Worksheet - 8

TOPIC: Work, Energy & Power

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#### SUMMARY

• Work – Measurement of work, Units of work done, Energy
• Different forms of energy, Kinetic energy, Potential energy
• Inter conversion of potential and kinetic energy
• Law of conservation of energy, Work energy theorem
• Power – definition and units, Electrical energy and Electrical power

#### SECTION I – OBJECTIVE

1. Work done upon a body is:
1. A vector quantity
2. A scalar quantity
3. (A) and (B) both are correct
4. None of these
2. Choose correct relation:
1. 1 J = 105 erg
2. 1 J = 107 erg
3. 1 J = 103 erg
4. None of these
3. Two bodies of mass 1 kg and 4 kg possess equal momentum. The ratio of their K.E.:
1. 4:1
2. 1:4
3. 2:1
4. 1:2
4. When you compress a spring you do work on it. The elastic potential energy of spring:
1. Increases
2. Decreases
3. Disappears
4. Remain constant
5. An object of mass 10 kg falls from height 10 m. Kinetic energy gained by the body will be approximately equal to:
1. 1000 J
2. 500 J
3. 100 J
4. None of these
6. A moving body need not have:
1. Potential energy
2. Kinetic energy
3. Momentum
4. Velocity
7. Chlorophyll in the plants convert the light energy into:
1. Heat energy
2. Chemical energy
3. Mechanical energy
4. Electrical energy
8. A weight lifter lifts 240 kg from the ground to a height of 2.5 m in 3 seconds his average power is:
1. 1960 W
2. 19.6 W
3. 1.96 W
4. 196 W
9. A body of mass 10 kg is dropped from a point where it possesses energy of 100 J. Then the K.E. when it reaches ground would be:
1. 1000 J
2. 100 J
3. 10 J
4. None of these
10. The power of pump which takes 10 s to lift 100 kg of water to fill a tank situated at height of 20 m is:
1. 2x104 N
2. 2x103 W
3. 2x102 W
4. None of these

#### SECTION II – SUBJECTIVE

1. Define:
1. (i) Work
2. (ii) Energy
3. (iii) Power
4. (iv) Kinetic energy.
2. State law of conservation of energy.
3. State work-energy theorem.
4. What is elastic potential energy?
5. A body of mass 10 kg is released from a height 10 m from the ground. After sometime its kinetic energy becomes 450 J. What will be the potential energy of the body at the instant?
6. Show that the mechanical energy of freely falling body is conserved.
7. What is the work to be done to increase the velocity of a car from 30 km/h to 60km/h, if the mass of the car is 1500kg.

### Solutions: to worksheet-8 Work, Energy & Power

#### Objective Problems:

 1.(B) 2.(B) 3.(A) 4.(A) 5.(A) 6.(A) 7.(B) 8.(A) 9.(B) 10.(B)

#### Subjective Problems

1. U = 550 J
2. W = 1.56 x 105 J