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MCQ practice · SSC Physics Board questions · Chapter 4: Work, Power and Energy

Chattogram Board 2024

If a body of mass 100 kg is lifted 20 m upward in 15 s, the quantities will be- which of the following is correct?

  1. i. 19600 J of work
  2. ii. 98 N of force
  3. iii. 1.31 kW of power

Think it through first, then pick an option.

  1. a i and ii
  2. b i and iii
  3. c ii and iii
  4. d i, ii and iii
Answer and explanation

Correct answer: b i and iii

i true: Work = weight × height = 100 × 9.8 × 20 = 19600 J. ii false: Lifting needs a force equal to the weight: 100 × 9.8 = 980 N, not 98 N. iii true: Power = work ÷ time = 19600 ÷ 15 = 1306.7 W ≈ 1.31 kW.

Why the other options are wrong

  • a i and ii: This is not the answer; the right combination is i and iii. i true: Work = weight × height = 100 × 9.8 × 20 = 19600 J. ii false: Lifting needs a force equal to the weight: 100 × 9.8 = 980 N, not 98 N. iii true: Power = work ÷ time = 19600 ÷ 15 = 1306.7 W ≈ 1.31 kW.
  • c ii and iii: This is not the answer; the right combination is i and iii. i true: Work = weight × height = 100 × 9.8 × 20 = 19600 J. ii false: Lifting needs a force equal to the weight: 100 × 9.8 = 980 N, not 98 N. iii true: Power = work ÷ time = 19600 ÷ 15 = 1306.7 W ≈ 1.31 kW.
  • d i, ii and iii: This is not the answer; the right combination is i and iii. i true: Work = weight × height = 100 × 9.8 × 20 = 19600 J. ii false: Lifting needs a force equal to the weight: 100 × 9.8 = 980 N, not 98 N. iii true: Power = work ÷ time = 19600 ÷ 15 = 1306.7 W ≈ 1.31 kW.