Two girls A and B each of weight 400 N, climb up the rope to a height of 8 m. Girl A takes 20 seconds while girl B takes 50 seconds to accomplish this task. What is the power expended by each girl?

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Solution

For girl A,
Weight of the girl, W = mg = 400 N
Distance travelled, h = 8 m
Time taken, t = 20 s
We know, power = $\frac{W o r k d o n e}{T i m e t a k e n}$ = $\frac{m g h}{t}$ = $\frac{400 \times 8}{20}$ = 160 W
For girl B,
Weight of the girl, W = mg = 400 N
Distance travelled, h = 8 m
Time taken, t = 50 s
We know, power = $\frac{W o r k d o n e}{T i m e t a k e n}$ = $\frac{m g h}{t}$ = $\frac{400 \times 8}{50}$ = 64 W

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