A girl of weight 440N climbs up a rope through a height of 7m in 20 sec. The power expended by the girl is?
Answers
weight of girl , W = 440N
girl climbs up a rope through a height of 7m.
finally, displacement covered by girl along weight , h = 7m
time taken by girl , t= 20 sec
so, power expended by the girl = weight of girl × displacement/time taken
= W × h/t
= 440 × 7/20
= 22 × 7 = 154 W
hence, power expended by the girl is 154W
Assuming that the girl is climbing the rope at a constant speed, Power is given by work done divided by time taken.For instance, P=wd/t.
From Newton's second law of motion,F=ma
The avarage force at which the girl is pulling on the rope, F=m×g=440N.
Therefore, work done=Force×Distance.
Worke done=440×7=3080 Joules
Hence, Power=w.d/t =3080/20 =154W
The power extended by the girl is 150W, since she was climbing the rope at a constant speed with an increasing potential energy.Therefore, her average power will be equivalent to work done (potential energy) divided by time.