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Work and Energy MCQs — Physics (page 3)

60 multiple-choice questions on Work and Energy from Physics, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

51. A 0.5 kg body falls from rest through 20 m and reaches 15 m/s. The work done against air resistance is (g = 9.8):

  1. 20.9 J
  2. 98 J
  3. 41.8 J
  4. 83.5 J

Answer: C) 41.8 J

Explanation: Loss of PE = mgh = 98 J; gain of KE = 56.2 J; work against friction = 41.8 J. SLO P-11-B-32 · Application

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52. Which of these is a conservative force?

  1. gravitational force
  2. viscous drag
  3. air resistance
  4. friction

Answer: A) gravitational force

Explanation: Work done by gravity depends only on height change. SLO P-11-B-31 · Understanding

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53. Air resistance on a falling body causes its total mechanical energy to:

  1. become infinite
  2. increase
  3. stay constant
  4. decrease

Answer: D) decrease

Explanation: Air drag is non-conservative. SLO P-11-B-31 · Understanding

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54. If the speed of a car is doubled, its kinetic energy becomes:

  1. 8 times as large
  2. half
  3. 4 times as large
  4. 2 times as large

Answer: C) 4 times as large

Explanation: K propto v^2. SLO P-11-B-29 · Application

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55. A constant force of 300 N acts through 0.2 m along its direction. On a force–displacement graph, the work done (area of the rectangle) is:

  1. 60 J
  2. 30 J
  3. 1500 J
  4. 120 J

Answer: A) 60 J

Explanation: W = Fd = 60 J. SLO P-11-B-30 · Application

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56. A 60 kg body moves at 5 m/s. Its kinetic energy is:

  1. 1500 J
  2. 375 J
  3. 750 J
  4. 150 J

Answer: C) 750 J

Explanation: K = 12mv^2 = 12(60)(5)^2 = 750 J. SLO P-11-B-29 · Application

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57. A body sliding up a rough slope loses kinetic energy to:

  1. gravitational PE only
  2. gravitational PE and work against friction
  3. friction only
  4. nothing

Answer: B) gravitational PE and work against friction

Explanation: Both take energy. SLO P-11-B-32 · Application

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58. When only conservative forces act, the total mechanical energy:

  1. increases
  2. becomes zero
  3. decreases
  4. is conserved

Answer: D) is conserved

Explanation: KE + PE is constant. SLO P-11-B-31 · Understanding

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59. A force of 10 N acts for the first 2 m, then 20 N for the next 3 m. The total work done is:

  1. 50 J
  2. 30 J
  3. 80 J
  4. 100 J

Answer: C) 80 J

Explanation: 10(2) + 20(3) = 20 + 60 = 80 J. SLO P-11-B-30 · Application

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60. A force of 25 N at 60^circ to the direction of motion moves a box 4 m. The work done is:

  1. 86.6 J
  2. 50 J
  3. 100 J
  4. 25 J

Answer: B) 50 J

Explanation: W = Fdcostheta = 25 4 0.5 = 50 J. SLO P-11-B-30 · Application

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