## Thursday, 27 October 2016

### 4 Work and Energy MCQs with solution

Chapter 4  Work and Energy is from Physics book of first year.

#### Work and Energy MCQs

Choose the correct one
2.            Which of the following forces do no work in displacing an object?
(a)                                                                         Frictional force                 (b) Gravitational force
(c) Electric force                       (d) centripetal force

3.            Work done in raising a body of weight w through height h is
(a)                                                                         wh                                   (b) 0
(c) -wh                                      (d) wh sin( thetha)

4.            The dimensions of work are

(a)                                                                         [MLT-1]                             (b) [MLT-2]
(c) [ML2T-1]                               (d) [ML2T-2]

5.            Work is said to negative when the angle between force and displacement is
(a)                                                                         90o                                   (b) 0o
(c) 180o                                    (d) between 90o and 180o

6.            When a vehicle is moving at constant velocity and a constant engine force is used to overcome friction, the product of force times velocity is a measure of
(a)                                                                         kinetic energy of the vehicle (b) work done by the vehicle (c) motive power of the vehicle (d) inertia of the vehicle.

7.            kWh is the unit of
(a)                                                                         power                                        (b)energy
(c) work                                    (d) electricity

8.            The dimensions of power are
(a)                                                                         [ML2T-1]                           (b) [ML2T-2]
(c) [ML2T-3]                               (d) [MLT-2

9.            A lift of mass 200 kg moves upward with uniform velocity of      4 ms-1. If the efficiency of the motor is 70 %, the input power of the motor is
(a)                                                                         11.2 kW                           (b) 16.7 kW
(c) 7.84 kW                              (d) 19.42 kW

10.         1 hp equals
(a)                                                                         746 J                               (b) 550 ft-lb
(c) 550 ft-lb s-1                         (d) 550 W

11.         The dimensions of kinetic energy are
(a)                                                                         [ML2T-2]                           (b) [ML-2T2]            (c) [ML2T-1]                          (d) [ ML2T-2]

12.         Two masses of 1 g and 4 g are moving with equal kinetic energies. The ratio of the magnitudes of their linear momenta is
(a)                                                                         4 : 1                               (b) 2 : 1
(c) 1 : 2                                    (d) 1 : 4

13.         A trolley of mass 60 kg moves on a frictionless horizontal surface and has a kinetic energy of 120 J. A mass of 20 kg is lowered vertically into the trolley. The total kinetic energy of the system is
(a)                                                                         60 J                                 (b) 72 J
(c) 120 J                                   (d) 144 J

14.         A bomb of 9 kg explodes into two pieces of masses 3 kg and 6 kg. The velocity of 3 kg mass is 16 ms-1. The kinetic energy of 6 kg mass will be
(a)                                                                         96 J                                 (b) 192 J
(c) 384 J                                   (d) none of these

15.         The potential energy of a 50 kg person jumping from a height of 10 m is
(a)                                                                         49 J                                 (b) 490 J
(c) 5000 J                                 (d) 500 J

16.         Which one of the followings is correct?
(a)                                                                         Watt and watt-hour represent the same quantities
(b)                                                                         Watt represents energy and watt-hour power
(c)                                                                         Watt represents power and watt-hour energy
(d)                                                                        none of these

17.         The dimensions of elastic potential energy are
(a)                                                                         [ML2T-2]                           (b) [ML-2T2]
(c) [ML2T-1]                         (d) [ ML2T-2]

20.         When two electrons come close to each other, their
(a)                                                                         KE change into electrical energy                   (b) KE change into PE
(c) electrical energy change into PE             (d) none of these

21.         A body is projected vertically from the surface of Earth of radius R with a velocity of equal to half the escape velocity. The maximum height gained by the body is
R                                              R
(a)                                                                         (b)
4                                              3
R
(c)                                              (d) R
2

22.         The intensity of solar energy intercepted by Earth at normal incidence daily is
(a)                                                                         1.4 kWm-2                                 (b) 14 kWm-2
(c) 1.0 kWm-2                                    (d) 0.14 kWm-2

23.         A long spring stretched by 2 cm has potential energy U. When stretched by 10 cm, its potential energy will be
(a)                                                                         5 U                                   (b) 2.5 U
U
(c) 25 U                                    (d)
5
24.         The expression for the escape velocity is given by
(a)                                                                         2gR2                               (b) 2gR
(c)          gR2                                  (d) 2gR
2
25.         An example of non-conservative force is
(a)                                                                         electric force                              (b) spring force
(c) frictional force                     (d) magnetic force

26.         Work-energy theorem can be expressed as
(a)                                                                         FaKf -Ki                          (b) Fv Kf2 -Ki2
(c) maKf2 -Ki2                          (d) FdKf -Ki

27.         1 kWh equals
(a)                                                                         0.36 MJ                           (b) 3.6 MJ
(c) 36 MJ                                  (d) 360 MJ

28.         If the mass and speed of a body are doubled, its kinetic energy becomes
(a)                                                                         3 times                            (b) 4 times
(c) 8 times                               (d) 16 times

29.         The absolute potential energy of a body at the surface of Earth
is
GmM                                        GmM
(a)                                                                         (b)
R                                             R2
GmM   GmM (c) -                                   (d) -
R                                              R2
30.         The absolute potential energy of a body in the gravitational
field of Earth is
(a)                                                                         directly proportional to the mass of the body
(b)                                                                         inversely proportional to the mass of the body
(c)                                                                         independent of the mass of the body
(d)                                                                        none of these

31.         The average and instantaneous powers become equal when
work is done at
(a)                                                                         any rate                           (b) constant rate
(c) increasing rate                    (d) decreasing rate

33.         The dimensions of work are the same as that of
(a)                                                                         torque                                       (b) momentum
(c) force                                   (d) power
34.         The muscular power of an athlete who spends 500 J of energy
to lift a load in 2 s is
(a)        125 W                                (b) 250 W
(c) 500 W                                 (d) 1000 W

35.         The value of escape velocity on the surface of Earth is
(a)                                                                         11.2 × 102 ms-1               (b) 11.2 × 103 ms-1
(c) 11.2 × 104 ms-1                  (d) 11.2 × 105 ms-1

36.         Tidal waves are produced due to the gravitational pull of
(a)                                                                         Earth                               (b) Sun
(c) Moon                                   (d) none of these

37.         The source of geothermal energy is the
(a)                                                                         rotation of Earth around the Sun
(b)                                                                         fusion in Sun
(d)                                                                        tidal energy

38.         Energy released in the process of fission and fusion is known
as:
(a)                                                                         geothermal energy                    (b) magnetic energy
(c) electrical energy                 (d) nuclear energy

39.         Solar cells are made of a material called
(a)                                                                         silicon                                        (b) iron
(c) carbon                                (d) aluminum

40.         The units of energy are the same as that of
(a)                                                                         force                               (b) power
(c) work                                    (d) torque

#### Answers to Test Chapter 4

 1 c 21 c 2 d 22 c 3 c 23 c 4 d 24 b 5 d 25 c 6 c 26 d 7 b 27 b 8 c 28 c 9 a 29 c 10 c 30 a 11 a 31 b 12 c 32 a 13 c 33 a 14 b 34 b 15 c 35 b 16 c 36 c 17 a 37 c 18 a 38 d 19 a 39 a 20 b 40 c