Lesson: Chapter 18 — Work, Energy and Power

18.3. Power 6 of 7 Reset answers

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Question 6

A child lifts a bag of mass 4 kg to a height of 1.5 m, and takes 3 seconds to do it. What is the child’s power? (g = 10 m s^-2, mixed exercise question 1)

A 60 W B 20 W C 180 W D 2 W

The right answer is the one marked above.

20 W. work = 4 kg × 10 m s^-2 × 1.5 m = 60 J. power = 60 J ÷ 3 s = 20 W.

60 W is the work with the wrong unit attached. The work is 60 joules; the power is 20 watts. Keeping the two apart is most of what this section asks of you.

Answer the question to continue.