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Worksheet on Work, Energy and Power

Q1 A 2 kg mass lying on a table is displaced in the horizontal direction through 50 cm. The work done by the normal reaction will be -


a) 0

b)100 joule

c)100 erg

d)10 joule



Q2 The work done against gravity in taking 10 kg. mass at 1 m height in 1 s will be :-


a) 49 J

b) 98 J

c)196 J

d) None of these



Q3 A force of 10N displace an object by 10m. If work done is 50J then direction of force make an angle with direction of displacement :-


a) 120 degree

b) 90 degree

c) 60 degree

d) None of these



Q4 If K.E. increases by 3%. Then momentum will increase by :-


a) 1.5%

b) 9%

c) 3%

d) 2%



Q5 If K.E. body is increased by 100%. Then % change in 'P'.


a) 50%

b) 41.4%

c) 10%

d) 20%



Q6 2 particles of mass 1 kg and 5 kg have same momentum, calculate ratio of their K.E.


a) 5 : 1

b) 25 : 1

c)1 : 1

d) 10 : 1



Q7 The kinetic energy of a body becomes four times of its initial value. The new linear momentum will be :-


a) Four times the initial value

b) Thrice the initial value

c) Twice the initial value

d) Same as the initial value



Q8 Two bodies of mass 1kg and 4kg have equal K.E. then the ratio of their momentum is :-


a) 2 : 1

b) 1 : 2

c) 4 : 1

d) 1 : 4



Q9 If the kinetic energy is increased by 300%, the momentum will increase by :-


a) 100%

b) 200%

c) 150%

d) 300%



Q10 If the kinetic energy of a body increases by 4% the momentum :


a) increases by 2%

b) increases by 4%

c) increases by 8%

d) increases by 16%



Q11 Which of the following statements is true for work done by conservative forces:-


a) It does not depend on path

b) It is equal to the difference of initial and final potential energy function

c) It can be recovered completely

d) All of the above



Q12 Which of the following statement is incorrect for a conservative field?


a) Work done in going from initial to final position is equal to change in kinetic energy of the particle.

b) Work done depends on path but not on initial and final positions.

c) Work done does not depend on path but depends only on initial and final positions

d) Work done on a particle in the field for a round trip is zero.



Q13 Which of the following is a non conservative force :-


a) Electric force

b) Gravitational force

c) Spring force

d) Viscous force



Q14 A spring of force constant 800 N/m has an extension of 5 cm. The work done in extending it from 5 cm to 15 cm is :-


a) 16 J

b) 8 J

c) 32 J

d) 24 J



Q15 A body of mass 2 kg falls from a height of 20 m. What is the loss in potential energy :-


a) 400 J

b) 300 J

c) 300 J

d) 100 J



Q16 A crane lifts 300 kg weight from earth's surface up to a height of 2m in 3 seconds. The average power generated by it will be -


a) 1960 W

b) 2205 w

c) 4410 W

d) 0 W



Q17 What average horsepower is developed by an 80kg man while climbing in 10 s flight of stairs that rises 6 m vertically ?


a) 0.63 hp

b) 1.26 hp

c) 1.8 hp

d) 2.1 hp



Q18 Assertion :- A spring has potential energy, when it is compressed (or stretched).

Reason :- In compressing or stretching, work is done on the spring against the restoring force which is stored as potential energy.


a) A

b) B

c) C

d) D



Q19 Assertion :- Work done by the force or against the force does not depend on path, then force is called conservative force.

Reason :- All central forces which follows the inverse square law are conservative forces.


a) A

b) B

c) C

d) D



Q20 Assertion :- A body can have energy without having momentum.

Reason :- A body can have momentum without having mechanical energy.


a) A

b) B

c) C

d) D



Q21 Assertion :- If work done by the force depends on path then force is said to be conservative.

Reason :- All the conservative forces are central force.


a) A

b) B

c) C

d) D



Q22 Assertion :- Frictional forces are conservative forces.

Reason :- Potential energy can be associated with frictional forces.


a) A

b) B

c) C

d) D



Q23 Assertion :- The change in kinetic energy of a particle is equal to the work done on it by the net force.

Reason :- Change in kinetic energy of particle is equal to the work done only in case of system of one particle.


a) A

b) B

c) C

d) D



Q24 Assertion :- Work done by or against gravitational force in moving a body from one point to another is independent of the actual path followed between the two points.

Reason :- Gravitational forces are conservative forces.


a) A

b) B

c) C

d) D



Q25 Assertion :- When a spring is elongated work done by spring is negative but when it compressed work done by spring is positive.

Reason :- Work done by spring is path dependent.


a) A

b) B

c) C

d) D



Q26 Assertion :- Work done by force of friction in moving a body in any round trip is zero.

Reason :- Frictional force is a conservative force.


a) A

b) B

c) C

d) D



Q27 Assertion :- Potential energy is possible only in conservative force field.

Reason :- Potential energy is a relative quantity but K.E. is an absolute quantity.


a) A

b) B

c) C

d) D



Q28 Assertion :- For an isolated system, mechanical energy is not conserved.

Reason :- For an isolated system internal energy is constant.


a) A

b) B

c) C

d) D



Q29 Assertion :- A truck and a car moving with the same kinetic energy are brought to rest by the application of breaks which provide equal retarding forces. Both come to rest in equal distance.

Reason :- It is possible that the speed of a body is zero but velocity is not zero.


a) A

b) B

c) C

d) D



Q30 Two ball bearings of mass m each moving in opposite directions with equal speeds v collide head on with each other. Predict the outcome of the collision, assuming it to be perfectly elastic..


a) v

b) 2v

c) v/2

d) v/4



Q31 A body of mass 4 kg initially at rest is subject to a force 16 N. What is the kinetic energy acquired by the body at the end of 10 s ?


a) 3250 J

b) 3200 J

c) 3150 J

d) 3100 J



Q32 If the linear momentum of a body increases by20%, what will be the % increase in the kinetic energy of the body?


a) 38%

b) 40%

c) 42%

d) 44%


Q33) Why a quick collision between two bodies is more violent then slow collision, even when initial and final velocities are equal?




ANSWERS

1) a

2) b

3) c

4) a

5) b

6) a

7) c

8) b

9) a

10) a

11) d

12) b

13 d

14) b

15) a

16) a

17) a

18) a

19) b

20) b

21) d

22) d

23) c

24) a

25) d

26) d

27) c

28) d

29) c

30) a

31) b

32) d

33) A quick collision between two bodies is more violent then slow collision, even when initial and final velocities are equal because the rate of change of momentum determines that the impulsive force small or large.











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