{"id":12451,"date":"2025-09-16T06:19:34","date_gmt":"2025-09-16T05:19:34","guid":{"rendered":"https:\/\/mcqsadda.com\/?p=12451"},"modified":"2025-10-22T09:33:32","modified_gmt":"2025-10-22T08:33:32","slug":"work-energy-and-power-top-100-mcqs-with-answer-and-explanation","status":"publish","type":"post","link":"https:\/\/mcqsadda.com\/index.php\/2025\/09\/16\/work-energy-and-power-top-100-mcqs-with-answer-and-explanation\/","title":{"rendered":"Work, Energy and Power Top 100 MCQs With Answer and Explanation"},"content":{"rendered":"\n

1. What is the SI unit of work?<\/mark><\/strong>
a) Joule
b) Watt
c) Newton
d) Pascal
Answer:<\/strong> a) Joule
Explanation:<\/strong> Work is force times displacement. Its unit is Newton \u00d7 meter = Joule (J).<\/p>\n\n\n\n

2. Work done is said to be zero when<\/mark><\/strong>
a) displacement is zero
b) force is zero
c) force and displacement are perpendicular
d) all of the above
Answer:<\/strong> d) all of the above
Explanation:<\/strong> Work done = F \u00d7 d \u00d7 cos\u03b8. If d=0, F=0, or \u03b8=90\u00b0, work done is zero.<\/p>\n\n\n\n

3. Work done by a conservative force depends on<\/mark><\/strong>
a) path taken
b) displacement only
c) initial and final positions
d) time
Answer:<\/strong> c) initial and final positions
Explanation:<\/strong> Work done by conservative forces depends only on initial and final positions, not the path.<\/p>\n\n\n\n

4. Which of the following is not a unit of power?<\/mark><\/strong>
a) Watt
b) Horsepower
c) Newton
d) Kilowatt
Answer:<\/strong> c) Newton
Explanation:<\/strong> Newton is a unit of force, not power.<\/p>\n\n\n\n

5. Power is defined as<\/mark><\/strong>
a) work done per unit time
b) force \u00d7 distance
c) force \u00d7 velocity
d) energy \u00d7 time
Answer:<\/strong> a) work done per unit time
Explanation:<\/strong> Power = Work \/ time<\/p>\n\n\n\n

6. The kinetic energy of a body is<\/mark><\/strong>
a) always positive
b) always negative
c) zero
d) none of the above
Answer:<\/strong> a) always positive
Explanation:<\/strong> Kinetic energy = \u00bdmv\u00b2, which is always positive.<\/p>\n\n\n\n

7. The potential energy of a body at ground level is taken as<\/mark><\/strong>
a) zero
b) one
c) negative
d) infinite
Answer:<\/strong> a) zero
Explanation:<\/strong> Potential energy at reference point (ground level) is usually taken as zero.<\/p>\n\n\n\n

8. The work-energy theorem states that<\/mark><\/strong>
a) work done is equal to change in kinetic energy
b) work done is equal to change in potential energy
c) work done is equal to total energy
d) none of the above
Answer:<\/strong> a) work done is equal to change in kinetic energy
Explanation:<\/strong> Work done on a body = change in kinetic energy.<\/p>\n\n\n\n

9. Which of the following is not a form of energy?<\/mark><\/strong>
a) Mechanical energy
b) Heat energy
c) Power
d) Electrical energy
Answer:<\/strong> c) Power
Explanation:<\/strong> Power is rate of doing work, not a form of energy.<\/p>\n\n\n\n

10. The unit of energy in CGS system is<\/mark><\/strong>
a) erg
b) joule
c) calorie
d) watt
Answer:<\/strong> a) erg
Explanation:<\/strong> 1 erg = 10\u207b\u2077 joules in CGS system<\/p>\n\n\n\n

11. The work done by friction is<\/mark><\/strong>
a) positive
b) zero
c) negative
d) depends on displacement
Answer:<\/strong> c) negative
Explanation:<\/strong> Friction opposes motion; hence work done by friction is negative.<\/p>\n\n\n\n

12. Which of the following quantities is scalar?<\/mark><\/strong>
a) Force
b) Work
c) Velocity
d) Displacement
Answer:<\/strong> b) Work
Explanation:<\/strong> Work is a scalar quantity.<\/p>\n\n\n\n

13. Potential energy of a mass m at height h is given by<\/mark><\/strong>
a) mgh
b) \u00bd mv\u00b2
c) mg\/h
d) 2mgh
Answer:<\/strong> a) mgh
Explanation:<\/strong> P<\/mark>otential energy = m \u00d7 g \u00d7 h.<\/p>\n\n\n\n

14. When a body is in free fall, its potential energy<\/mark><\/strong>
a) increases
b) decreases
c) remains constant
d) becomes zero instantly
Answer:<\/strong> b) decreases
Explanation:<\/strong> As height decreases, potential energy decreases.<\/p>\n\n\n\n

15. The work done in moving a charge q across a potential difference V is<\/mark><\/strong>
a) qV
b) q\/V
c) V\/q
d) q + V
Answer:<\/strong> a) qV
Explanation:<\/strong> Work done = charge \u00d7 potential difference<\/p>\n\n\n\n

16. The dimension of power is<\/mark><\/strong>
a) MLT\u207b\u00b2
b) ML\u00b2T\u207b\u00b3
c) MLT\u207b\u00b9
d) M\u00b2L\u00b2T\u207b\u00b2
Answer:<\/strong> b) ML\u00b2T\u207b\u00b3
Explanation:<\/strong> Power = energy\/time = ML\u00b2T\u207b\u00b2 \/ T = ML\u00b2T\u207b\u00b3.<\/p>\n\n\n\n

17. Which of the following has the greatest kinetic energy?<\/mark><\/strong>
a) 1 kg mass moving at 10 m\/s
b) 2 kg mass moving at 5 m\/s
c) 0.5 kg mass moving at 20 m\/s
d) 1.5 kg mass moving at 8 m\/s
Answer:<\/strong> c) 0.5 kg mass moving at 20 m\/s
Explanation:<\/strong> KE = \u00bd mv\u00b2. Calculate for each to compare.<\/p>\n\n\n\n

18. The rate of change of work done is called<\/mark><\/strong>
a) Energy
b) Power
c) Force
d) Momentum
Answer:<\/strong> b) Power
Explanation:<\/strong> Power = dW\/dt.<\/p>\n\n\n\n

19. Which of these is a non-conservative force?<\/mark><\/strong>
a) Gravitational force
b) Elastic spring force
c) Frictional force
d) Electrostatic force
Answer:<\/strong> c) Frictional force
Explanation:<\/strong> Friction depends on path and dissipates energy.<\/p>\n\n\n\n

20. Work done in lifting a body is equal to<\/mark><\/strong>
a) increase in potential energy
b) increase in kinetic energy
c) decrease in potential energy
d) none of these
Answer:<\/strong> a) increase in potential energy
Explanation:<\/strong> Work done against gravity increases PE.<\/p>\n\n\n\n

21. The work done by a force of 10 N in moving a body 3 m in the direction of force is<\/mark><\/strong>
a) 13 J
b) 30 J
c) 7 J
d) 3 J
Answer:<\/strong> b) 30 J
Explanation:<\/strong> Work = Force \u00d7 displacement = 10 \u00d7 3 = 30 J.<\/p>\n\n\n\n

22. If the displacement is doubled and force remains constant, work done<\/mark><\/strong>
a) doubles
b) halves
c) remains the same
d) quadruples
Answer:<\/strong> a) doubles
Explanation:<\/strong> Work \u221d displacement (if force constant).<\/p>\n\n\n\n

23. The kinetic energy of a body is doubled. Its velocity is multiplied by<\/mark><\/strong>
a) \u221a2
b) 2
c) 4
d) 1\/\u221a2
Answer:<\/strong> a) \u221a2
Explanation:<\/strong> KE = \u00bd mv\u00b2, so doubling KE means velocity multiplied by \u221a2.<\/p>\n\n\n\n

24. Power developed by a machine which does 500 J of work in 5 seconds is<\/mark><\/strong>
a) 100 W
b) 2500 W
c) 5 W
d) 50 W
Answer:<\/strong> a) 100 W
Explanation:<\/strong> Power = Work \/ time = 500\/5 = 100 W.<\/p>\n\n\n\n

25. Which of the following is true for conservative forces?<\/mark><\/strong>
a) Work done depends on path
b) Work done is zero in a closed path
c) Energy is not conserved
d) Work done depends on velocity
Answer:<\/strong> b) Work done is zero in a closed path
Explanation:<\/strong> Conservative forces do zero net work in closed paths.<\/p>\n\n\n\n

26. A body is thrown vertically upwards. At the highest point, its kinetic energy is<\/mark><\/strong>
a) maximum
b) zero
c) minimum but not zero
d) equal to potential energy
Answer:<\/strong> b) zero
Explanation:<\/strong> At the highest point velocity = 0, so kinetic energy = 0.<\/p>\n\n\n\n

27. A body of mass 2 kg is moving with a speed of 3 m\/s. Its kinetic energy is<\/mark><\/strong>
a) 9 J
b) 18 J
c) 6 J
d) 3 J
Answer:<\/strong> b) 9 J
Explanation:<\/strong> KE = \u00bd \u00d7 2 \u00d7 3\u00b2 = 9 J.<\/p>\n\n\n\n

28. Work done by gravity on a free-falling body is<\/mark><\/strong>
a) positive
b) negative
c) zero
d) none of these
Answer:<\/strong> a) positive
Explanation:<\/strong> Gravity acts in the direction of displacement, so work done is positive.<\/p>\n\n\n\n

29. The work done on a body is negative when<\/mark><\/strong>
a) force is zero
b) displacement is zero
c) force and displacement are in opposite directions
d) force and displacement are perpendicular
Answer:<\/strong> c) force and displacement are in opposite directions
Explanation:<\/strong> Work = F \u00d7 d \u00d7 cos\u03b8. If \u03b8=180\u00b0, work is negative.<\/p>\n\n\n\n

30. Which of the following has the least power?<\/mark><\/strong>
a) Doing 100 J work in 1 sec
b) Doing 200 J work in 4 sec
c) Doing 300 J work in 6 sec
d) Doing 400 J work in 8 sec
Answer:<\/strong> d) Doing 400 J work in 8 sec
Explanation:<\/strong> Power = Work\/Time. Calculate to compare<\/p>\n\n\n\n

31. The total mechanical energy of a freely falling body remains<\/mark><\/strong>
a) constant
b) increases
c) decreases
d) first increases then decreases
Answer:<\/strong> a) constant
Explanation:<\/strong> In absence of air resistance, mechanical energy is conserved.<\/p>\n\n\n\n

32. The rate of change of kinetic energy is equal to<\/mark><\/strong>
a) force \u00d7 velocity
b) force \u00d7 displacement
c) power \u00d7 time
d) force \/ velocity
Answer:<\/strong> a) force \u00d7 velocity
Explanation:<\/strong> Rate of change of KE = Power = F \u00d7 v.<\/p>\n\n\n\n

33. Which of the following represents energy stored due to position?<\/mark><\/strong>
a) Kinetic energy
b) Potential energy
c) Thermal energy
d) Sound energy
Answer:<\/strong> b) Potential energy
Explanation:<\/strong> Potential energy depends on position or configuration.<\/p>\n\n\n\n

34. The power of a machine increases when<\/mark><\/strong>
a) more work is done in less time
b) less work is done in more time
c) work done remains constant
d) none of these
Answer:<\/strong> a) more work is done in less time
Explanation:<\/strong> Power = Work \/ time.<\/p>\n\n\n\n

35. The work done by the tension in a string during circular motion is<\/mark><\/strong>
a) positive
b) zero
c) negative
d) depends on speed
Answer:<\/strong> b) zero
Explanation:<\/strong> Tension acts perpendicular to displacement in circular motion.<\/p>\n\n\n\n

36. The energy possessed by a body due to its motion is called<\/mark><\/strong>
a) potential energy
b) kinetic energy
c) thermal energy
d) nuclear energy
Answer:<\/strong> b) kinetic energy
Explanation:<\/strong> Kinetic energy is energy due to motion.<\/p>\n\n\n\n

37. The unit of work done in the CGS system is<\/mark><\/strong>
a) Joule
b) Erg
c) Newton
d) Watt
Answer:<\/strong> b) Erg
Explanation:<\/strong> Erg is CGS unit of work (1 erg = 10\u207b\u2077 J).<\/p>\n\n\n\n

38. Which of the following is a vector quantity?<\/mark><\/strong>
a) Work
b) Energy
c) Power
d) Force
Answer:<\/strong> d) Force
Explanation:<\/strong> Force is a vector, others are scalars.<\/p>\n\n\n\n

39. If the force applied on a body is doubled, then the work done (for same displacement) will be<\/mark><\/strong>
a) halved
b) doubled
c) quadrupled
d) same
Answer:<\/strong> b) doubled
Explanation:<\/strong> Work done is directly proportional to force.<\/p>\n\n\n\n

40. The work done in compressing a spring by x is proportional to<\/mark><\/strong>
a) x
b) x\u00b2
c) \u221ax
d) 1\/x
Answer:<\/strong> b) x\u00b2
Explanation:<\/strong> Work done on spring = \u00bd k x\u00b2.<\/p>\n\n\n\n

41. The energy which is stored and can be converted into work is called<\/mark><\/strong>
a) kinetic energy
b) potential energy
c) thermal energy
d) sound energy
Answer:<\/strong> b) potential energy
Explanation:<\/strong> Potential energy is stored energy.<\/p>\n\n\n\n

42. The unit of power is<\/mark><\/strong>
a) Newton
b) Watt
c) Joule
d) Erg
Answer:<\/strong> b) Watt
Explanation:<\/strong> Power = Joule \/ second = Watt.<\/p>\n\n\n\n

43. If work done on a body is zero, then its kinetic energy<\/mark><\/strong>
a) increases
b) decreases
c) remains constant
d) none of these
Answer:<\/strong> c) remains constant
Explanation:<\/strong> Zero work means no change in kinetic energy.<\/p>\n\n\n\n

44. The dimension of work is<\/mark><\/strong>
a) M L\u00b2 T\u207b\u00b2
b) M L T\u207b\u00b9
c) M L T\u207b\u00b2
d) M L\u00b2 T\u207b\u00b3
Answer:<\/strong> a) M L\u00b2 T\u207b\u00b2
Explanation:<\/strong> Work = force \u00d7 distance = MLT\u207b\u00b2 \u00d7 L = ML\u00b2T\u207b\u00b2.<\/p>\n\n\n\n

45. Which of the following is a scalar quantity?<\/mark><\/strong>
a) Displacement
b) Velocity
c) Work done
d) Acceleration
Answer:<\/strong> c) Work done
Explanation:<\/strong> Work done is scalar, others are vectors.<\/p>\n\n\n\n

46. The efficiency of a machine can be more than<\/mark><\/strong>
a) 100%
b) 90%
c) 80%
d) 60%
Answer:<\/strong> b) 90%
Explanation:<\/strong> Efficiency >100% violates conservation of energy, so practically less than 100%.<\/p>\n\n\n\n

47. When potential energy decreases, kinetic energy<\/mark><\/strong>
a) increases
b) decreases
c) remains constant
d) none of the above
Answer:<\/strong> a) increases
Explanation:<\/strong> Mechanical energy conserved, so decrease in PE means increase in KE.<\/p>\n\n\n\n

48. The potential energy of a body depends on<\/mark><\/strong>
a) its mass and velocity
b) its velocity and height
c) its mass and height
d) its velocity only
Answer:<\/strong> c) its mass and height
Explanation:<\/strong> PE = mgh.<\/p>\n\n\n\n

49. When a body is thrown upwards, its total energy at the highest point is<\/mark><\/strong>
a) kinetic energy
b) potential energy
c) zero
d) none of these
Answer:<\/strong> b) potential energy
Explanation:<\/strong> At highest point, KE = 0, all energy is PE.<\/p>\n\n\n\n

50. Which of the following quantities remains constant during free fall (ignoring air resistance)?<\/mark><\/strong>
a) Potential energy
b) Kinetic energy
c) Mechanical energy
d) None of these
Answer:<\/strong> c) Mechanical energy
Explanation:<\/strong> Sum of KE and PE is conserved.<\/p>\n\n\n\n

51. The work done in stretching a spring is proportional to<\/mark><\/strong>
a) extension
b) square of extension
c) cube of extension
d) inverse of extension
Answer:<\/strong> b) square of extension
Explanation:<\/strong> Work done = \u00bd k x\u00b2 (Hooke\u2019s law).<\/p>\n\n\n\n

52. If velocity of a body is doubled, its kinetic energy becomes<\/mark><\/strong>
a) doubled
b) quadrupled
c) halved
d) remains same
Answer:<\/strong> b) quadrupled
Explanation:<\/strong> KE = \u00bd mv\u00b2, doubling v makes KE 4 times.<\/p>\n\n\n\n

53. Which force does positive work on a falling object?<\/mark><\/strong>
a) Friction
b) Gravity
c) Tension
d) Normal force
Answer:<\/strong> b) Gravity
Explanation:<\/strong> Gravity acts downward, same as displacement, doing positive work.<\/p>\n\n\n\n

54. Which of these is not a scalar quantity?<\/mark><\/strong>
a) Work
b) Energy
c) Power
d) Force
Answer:<\/strong> d) Force
Explanation:<\/strong> Force is a vector quantity.<\/p>\n\n\n\n

55. Power is measured in watts, where 1 watt =<\/mark><\/strong>
a) 1 joule\/second
b) 1 newton\/second
c) 1 joule\/minute
d) 1 newton \u00d7 meter
Answer:<\/strong> a) 1 joule\/second
Explanation:<\/strong> Power = Work \/ time, unit is Joule per second.<\/p>\n\n\n\n

56. The kinetic energy of a body is 100 J. If its velocity is doubled, the kinetic energy becomes<\/mark><\/strong>
a) 100 J
b) 200 J
c) 400 J
d) 50 J
Answer:<\/strong> c) 400 J
Explanation:<\/strong> KE \u221d v\u00b2, so doubling velocity quadruples KE.<\/p>\n\n\n\n

57. Work done by frictional force is<\/mark><\/strong>
a) positive
b) zero
c) negative
d) infinite
Answer:<\/strong> c) negative
Explanation:<\/strong> Friction opposes motion, so work done is negative.<\/p>\n\n\n\n

58. Which of the following is an example of conservative force?<\/mark><\/strong>
a) Frictional force
b) Tension force
c) Gravitational force
d) Air resistance
Answer:<\/strong> c) Gravitational force
Explanation:<\/strong> Gravitational force is path independent and conservative.<\/p>\n\n\n\n

59. A machine lifts a weight of 50 N through a height of 4 m in 2 seconds. Power developed is<\/mark><\/strong>
a) 25 W
b) 100 W
c) 200 W
d) 400 W
Answer:<\/strong> b) 100 W
Explanation:<\/strong> Work = Force \u00d7 height = 50 \u00d7 4 = 200 J; Power = 200\/2 = 100 W.<\/p>\n\n\n\n

60. Which of the following quantities has the unit kg\u00b7m\/s\u00b2?<\/mark><\/strong>
a) Work
b) Power
c) Force
d) Energy
Answer:<\/strong> c) Force
Explanation:<\/strong> Newton = kg\u00b7m\/s\u00b2 is the unit of force.<\/p>\n\n\n\n

61. Work done by the gravitational force on a satellite moving in a circular orbit is<\/mark><\/strong>
a) positive
b) negative
c) zero
d) depends on speed
Answer:<\/strong> c) zero
Explanation:<\/strong> Gravitational force is perpendicular to displacement in circular orbit.<\/p>\n\n\n\n

62. Which form of energy is associated with the motion of particles?<\/mark><\/strong>
a) Potential energy
b) Kinetic energy
c) Thermal energy
d) Nuclear energy
Answer:<\/strong> b) Kinetic energy
Explanation:<\/strong> Kinetic energy relates to motion.<\/p>\n\n\n\n

63. The work done in moving a body around a closed path by a conservative force is<\/mark><\/strong>
a) zero
b) positive
c) negative
d) depends on path
Answer:<\/strong> a) zero
Explanation:<\/strong> Work by conservative forces over a closed path is zero.<\/p>\n\n\n\n

64. The work done by the force in moving a body from rest to speed v is equal to<\/mark><\/strong>
a) potential energy
b) kinetic energy
c) total energy
d) momentum
Answer:<\/strong> b) kinetic energy
Explanation:<\/strong> Work done changes kinetic energy from zero to \u00bd mv\u00b2.<\/p>\n\n\n\n

65. The work done when a force acts perpendicular to displacement is<\/mark><\/strong>
a) maximum
b) minimum
c) zero
d) negative
Answer:<\/strong> c) zero
Explanation:<\/strong> Work done = F \u00d7 d \u00d7 cos\u03b8; cos90\u00b0=0 means no work done.<\/p>\n\n\n\n

66. Which of these quantities is NOT conserved in the presence of friction?<\/mark><\/strong>
a) Kinetic energy
b) Mechanical energy
c) Potential energy
d) Mass
Answer:<\/strong> b) Mechanical energy
Explanation:<\/strong> Mechanical energy is lost due to friction (converted to heat).<\/p>\n\n\n\n

67. The work done by a force in displacing a body is 100 J. If the displacement is doubled, then work done becomes<\/mark><\/strong>
a) 50 J
b) 100 J
c) 200 J
d) 400 J
Answer:<\/strong> c) 200 J
Explanation:<\/strong> Work done \u221d displacement (if force constant).<\/p>\n\n\n\n

68. Energy can neither be created nor destroyed according to<\/mark><\/strong>
a) Newton\u2019s law
b) Law of conservation of energy
c) Pascal\u2019s law
d) Bernoulli\u2019s principle
Answer:<\/strong> b) Law of conservation of energy
Explanation:<\/strong> Energy is conserved in an isolated system.<\/p>\n\n\n\n

69. The potential energy stored in a stretched spring is 10 J. When it is released, this energy transforms into<\/mark><\/strong>
a) kinetic energy
b) thermal energy
c) potential energy of the body
d) mechanical energy
Answer:<\/strong> a) kinetic energy
Explanation:<\/strong> Stored potential energy converts into kinetic energy when released.<\/p>\n\n\n\n

70. The dimensions of power are<\/mark><\/strong>
a) M L\u00b2 T\u207b\u00b2
b) M L\u00b2 T\u207b\u00b3
c) M L T\u207b\u00b9
d) M L T\u207b\u00b2
Answer:<\/strong> b) M L\u00b2 T\u207b\u00b3
Explanation:<\/strong> Power = Energy \/ time = ML\u00b2T\u207b\u00b2 \/ T = ML\u00b2T\u207b\u00b3.<\/p>\n\n\n\n

71. The unit of work done is the same as that of<\/mark><\/strong>
a) force
b) energy
c) power
d) momentum
Answer:<\/strong> b) energy
Explanation:<\/strong> Work and energy have the same units (Joule).<\/p>\n\n\n\n

72. A machine does 500 J of work in 10 seconds. The power output is<\/mark><\/strong>
a) 50 W
b) 5 W
c) 5000 W
d) 500 W
Answer:<\/strong> a) 50 W
Explanation:<\/strong> Power = Work \/ time = 500 \/ 10 = 50 W.<\/p>\n\n\n\n

73. The work done by the force of friction is negative because<\/mark><\/strong>
a) friction acts in direction of motion
b) friction acts opposite to displacement
c) friction is a conservative force
d) friction increases mechanical energy
Answer:<\/strong> b) friction acts opposite to displacement
Explanation:<\/strong> Force and displacement are in opposite directions.<\/p>\n\n\n\n

74. Which of the following is an example of non-mechanical energy?<\/mark><\/strong>
a) Kinetic energy
b) Potential energy
c) Electrical energy
d) Elastic energy
Answer:<\/strong> c) Electrical energy
Explanation:<\/strong> Electrical energy involves charges and fields, not mechanical motion.<\/p>\n\n\n\n

75. The work done on a body moving on a frictionless horizontal surface by a constant force is<\/mark><\/strong>
a) equal to change in kinetic energy
b) zero
c) negative
d) equal to change in potential energy
Answer:<\/strong> a) equal to change in kinetic energy
Explanation:<\/strong> Work done changes kinetic energy.<\/p>\n\n\n\n

76. The power of a motor which lifts a load of 200 N through 10 m in 20 seconds is<\/mark><\/strong>
a) 10 W
b) 100 W
c) 200 W
d) 20 W
Answer:<\/strong> d) 100 W
Explanation:<\/strong> Work = 200 \u00d7 10 = 2000 J, Power = 2000 \/ 20 = 100 W.<\/p>\n\n\n\n

77. Which of the following is a non-conservative force?<\/mark><\/strong>
a) Gravitational force
b) Electrostatic force
c) Frictional force
d) Spring force
Answer:<\/strong> c) Frictional force
Explanation:<\/strong> Friction depends on path and dissipates energy as heat.<\/p>\n\n\n\n

78. Work done by a force is positive when the angle between force and displacement is<\/mark><\/strong>
a) 90\u00b0
b) 180\u00b0
c) 0\u00b0
d) 45\u00b0
Answer:<\/strong> c) 0\u00b0
Explanation:<\/strong> cos 0\u00b0 = 1, maximum positive work done.<\/p>\n\n\n\n

79. Which of the following quantities is vector?<\/mark><\/strong>
a) Work
b) Energy
c) Displacement
d) Power
Answer:<\/strong> c) Displacement
Explanation:<\/strong> Displacement has magnitude and direction.<\/p>\n\n\n\n

80. The kinetic energy of an object moving with speed v is K. Its kinetic energy when speed is 3v will be<\/mark><\/strong>
a) 3K
b) 6K
c) 9K
d) K\/3
Answer:<\/strong> c) 9K
Explanation:<\/strong> KE \u221d v\u00b2, so KE becomes 9 times.<\/p>\n\n\n\n

81. The SI unit of work is named after<\/mark><\/strong>
a) Newton
b) Watt
c) Joule
d) Pascal
Answer:<\/strong> c) Joule
Explanation:<\/strong> Work unit is named after James Prescott Joule.<\/p>\n\n\n\n

82. Power is maximum when<\/mark><\/strong>
a) force and velocity are in same direction
b) force and velocity are perpendicular
c) force is zero
d) velocity is zero
Answer:<\/strong> a) force and velocity are in same direction
Explanation:<\/strong> Power = F \u00d7 v \u00d7 cos\u03b8; max when \u03b8=0\u00b0.<\/p>\n\n\n\n

83. Which of the following is not a unit of power?<\/mark><\/strong>
a) Watt
b) Horsepower
c) Joule
d) Erg\/s
Answer:<\/strong> c) Joule
Explanation:<\/strong> Joule is energy, not power.<\/p>\n\n\n\n

84. The work done by normal force on a body resting on a surface is<\/mark><\/strong>
a) positive
b) negative
c) zero
d) depends on motion
Answer:<\/strong> c) zero
Explanation:<\/strong> Normal force is perpendicular to displacement.<\/p>\n\n\n\n

85. The energy possessed by a body due to its configuration or position is called<\/mark><\/strong>
a) kinetic energy
b) potential energy
c) heat energy
d) sound energy
Answer:<\/strong> b) potential energy
Explanation:<\/strong> Potential energy depends on position\/configuration.<\/p>\n\n\n\n

86. The kinetic energy of an object depends on<\/mark><\/strong>
a) mass and velocity
b) only mass
c) only velocity
d) neither mass nor velocity
Answer:<\/strong> a) mass and velocity
Explanation:<\/strong> KE = \u00bd mv\u00b2 depends on both.<\/p>\n\n\n\n

87. Work done by gravitational force on an object moving vertically upwards is<\/mark><\/strong>
a) positive
b) negative
c) zero
d) depends on speed
Answer:<\/strong> b) negative
Explanation:<\/strong> Force and displacement are in opposite directions.<\/p>\n\n\n\n

88. The unit of work in the CGS system is<\/mark><\/strong>
a) Joule
b) Erg
c) Watt
d) Newton
Answer:<\/strong> b) Erg
Explanation:<\/strong> Erg is CGS unit of work (1 erg = 10\u207b\u2077 Joule).<\/p>\n\n\n\n

89. A body moving with uniform velocity does<\/mark><\/strong>
a) positive work
b) negative work
c) zero work
d) infinite work
Answer:<\/strong> c) zero work
Explanation:<\/strong> Force is zero, so work done is zero.<\/p>\n\n\n\n

90. The rate at which work is done is called<\/mark><\/strong>
a) energy
b) power
c) force
d) momentum
Answer:<\/strong> b) power
Explanation:<\/strong> Power = work done \/ time.<\/p>\n\n\n\n

91. The energy possessed by a body due to its motion is<\/mark><\/strong>
a) potential energy
b) kinetic energy
c) thermal energy
d) nuclear energy
Answer:<\/strong> b) kinetic energy
Explanation:<\/strong> Kinetic energy is energy due to motion.<\/p>\n\n\n\n

92. Which of the following quantities is scalar?<\/mark><\/strong>
a) Force
b) Velocity
c) Work done
d) Displacement
Answer:<\/strong> c) Work done
Explanation:<\/strong> Work done has magnitude only.<\/p>\n\n\n\n

93. The power of an engine is the rate of<\/mark><\/strong>
a) doing work
b) changing force
c) changing displacement
d) changing velocity
Answer:<\/strong> a) doing work
Explanation:<\/strong> Power = work done \/ time.<\/p>\n\n\n\n

94. The unit of power in the CGS system is<\/mark><\/strong>
a) erg\/sec
b) watt
c) joule
d) newton
Answer:<\/strong> a) erg\/sec
Explanation:<\/strong> CGS unit of power is erg\/second.<\/p>\n\n\n\n

95. Work done by a force of 10 N in moving a body 2 m is 20 J. The force acts at an angle of<\/mark><\/strong>
a) 0\u00b0
b) 30\u00b0
c) 60\u00b0
d) 90\u00b0
Answer:<\/strong> a) 0\u00b0
Explanation:<\/strong> Work = F \u00d7 d \u00d7 cos\u03b8 = 10 \u00d7 2 \u00d7 cos\u03b8 = 20 \u21d2 cos\u03b8=1 \u21d2 \u03b8=0\u00b0.<\/p>\n\n\n\n

96. The kinetic energy of a body of mass m and velocity v is<\/mark><\/strong>
a) mv
b) \u00bd mv\u00b2
c) mv\u00b2
d) 2mv\u00b2
Answer: b) \u00bd mv\u00b2
Explanation: Standard formula for kinetic energy.<\/p>\n\n\n\n

97. A machine does 500 J of work in 5 seconds. Its power output is<\/mark><\/strong>
a) 50 W
b) 100 W
c) 25 W
d) 10 W
Answer:<\/strong> b) 100 W
Explanation:<\/strong> Power = Work \/ time = 500 \/ 5 = 100 W.<\/p>\n\n\n\n

98. The unit of energy is the same as<\/mark><\/strong>
a) unit of force
b) unit of power
c) unit of work
d) unit of velocity
Answer:<\/strong> c) unit of work
Explanation:<\/strong> Energy and work have the same unit, joule.<\/p>\n\n\n\n

99. The force which does no work is<\/mark><\/strong>
a) friction
b) gravitational force
c) tension in a string during circular motion
d) applied force
Answer:<\/strong> c) tension in a string during circular motion
Explanation:<\/strong> Tension is perpendicular to displacement in circular motion.<\/p>\n\n\n\n

100. The power of a machine is the rate of<\/mark><\/strong>
a) doing work
b) change in energy
c) change in force
d) displacement
Answer:<\/strong> a) doing work
Explanation:<\/strong> Power is defined as rate of doing work.<\/p>\n","protected":false},"excerpt":{"rendered":"

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