he role of "man" is to just stop it from getting accelerated
let F be the force by man up along >.
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net force on block = m a (down) = mg sin 28 - F - uk(mg cos 28)
since acceleration a = 0
mg sin 28 = F + uk(mg cos 28)
F = mg[sin28 - 0.4 cos 28] = 376.1 N
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work done by man = F * d cos 180 = - F *3.6 = - 1353.96 J
-ve sign because F and displacement are 180 deg apart
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work done by friction = - 0.4 {mg cos 28} * 3.6 = - 4111.85 J
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work done by gravity = + {mg sin 28} * 3.6 = 5465.78 J
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net work done = net force *3.6 = 0 *3.6 = 0
there is no net force on piano
net work done = 5465.78 - 1353.96 - 4111.85 = 0 (very very close to zero) because decimal places??
