At what minimum rate is a 60.0-kg boy using energy when, in 8.00 s, he runs up a flight of stairs that is 10.0-m high?

The answer is 735 W.

He runs up the stairs, so he needs a total amount of energy = mgh = 5880 Joules. For the rate: since he goes from zero energy to 5880 Joules over 8 seconds... Joules/sec = 5,880/8 = 735 W

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