Two girls each of weigth 400N, climb up a rope through a height of 8m. We name one of the girls A and the other B. Girl A takes 20s while B takes 50s to accomplish this task. What is the power expneded by each girl.

Explanation

(i) Power expended by girl A:
Weight of the girl, `mg = 400 N`
Displacement (height), `h = 8 m`
Time taken, `t = 20 s`
From Eq. (11.8),

Power, P = Work done/time taken
`= (mgh)/(t)`
`= (400 N xx 8m)/(20 s)`
`160 W`
(ii) Power expended by girl B: Weight of the girl, `mg = 400 N` Displacement (height), `h = 8 m` Time taken, `t = 50 s`
Power, `P = (mgh)/(t)`
`= (400 N xx 8m)/(50 s)`
`= 64 W`
Power expended by girl A is `160 W`.
Power expended by girl B is `64 W`.