Q:You lift a 30.60-kg box from the floor onto a shelf 0.82m above the floor. If

Question

Q:You lift a 30.60-kg box from the floor onto a shelf 0.82m above the floor. If you lift the box with a constant speed, what is the force you exert on the box? Is it upward or downward? (You must answer both parts to get credit.)

Q:What is the work you do on the box?(make sure you get the right sign)

Q:What is the magnitude of the change in potential energy of the box? Does it increase or decrease? (You must answer both correctly to get credit.)

*Consider what your answers would be if you lower the box back to the floor. You do not need to enter the answers for this, but you do need to know what signs might change for the opposite case.

Explanation / Answer

box weight = 30.60 kg

constant speed means no acceleration so F = mg = 306 N

work = F*s = 306 *0.82 = 250.92 Nm

change in PE is Final - initial = mg(H2 -H1) = 306 * (0.82 -0) = 250.92J

positive PE

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