From Giancoli\'s 5th edition book (pg. 174 #10): A 280kg piano slides 4.3m down

Question

From Giancoli's 5th edition book (pg. 174 #10):

A 280kg piano slides 4.3m down a 30 degree incline and is kept fromaccelerating by a man who is pushing back on it parallel to theincline. The coefficeint of kinetic friction is .40. Calculate thework done by force of gravity and the net work done by the man onthe piano.

ANSWER: Wg = 5.9 x 10^3 J
ANSWER: W= 0

I'm confident about finding the work done by applied force andfrictional force but how does one calculate the work of gravity?Isn't it just 0? Also which works should be added for W? Doesit include Normal force and gravity force?

Thanks for any help you can give me!

Explanation / Answer

m = 280 kg, d = 4.3 m, = 30o, = 0.40. Wg = mg*d*cos(90 - ) = 5.90*103 J W = 0 (because no acceleration, kinetic energy does notchange)

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