Question

A 45 kg student runs up a flight of stairs that are 3.2 m high in 2 seconds. How much power did the student use during this time?
706 W
288 W
72 W
7.0 W

Answer 1

Power = work done/time. Work done by gravity = mgh = 45x9.8x3.2 = 1411.2J. Therefore, power = 1411.2/2 = 705.6 ~ 706W.

Answer 2

Power=Work/time.
In this case Work=increase in potential energy.
Supposing he was initially on the floor, W=mgh=45*9.8*3.2=1411.2 J.
Therefore
Power=1411.2/2=705.6≈706 W.