# Physics - pulley

A construction crew pulls up an 87.5-kg load using a rope thrown over a pulley and pulled by an electric motor. They lift the load 15.5 m and it arrives with a speed of 15.6 m/s having started from rest. Assume that acceleration was not constant.

I have done the problem but am thinking that it is wrong. Can anyone please check my work and correct me? Thank you so much.

a) How much work (J) was done by the motor?

My work: (87.5 kg)(15.5 m) = 1356.3 J
K= 1/2(87.5 kg)(15.6 m/s)^2 = 10647
1356.3 + 10647 = 12003.25 J

b) How much work (J) was done by gravity?

My work: - 1356.25 J

c) What constant force (N) could the motor have exerted to cause this motion? (This would have been the average force exerted by the motor)

My work: (12003.25) = (f)(15.5m)

12003.25J/15.5 = 774.4 N

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1. This is way back ago, but for those students who are encountering the same problem,

Work done = PE + KE = mgh + .5mv^2

And he is missing h for PE

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