1. You lift a 48.10-kg box from the floor onto a shelf 0.79m above the floor. If
ID: 1330938 • Letter: 1
Question
1. You lift a 48.10-kg box from the floor onto a shelf 0.79m 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?
2. What is the work you do on the box?(make sure you get the right sign)
3. 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
1) Force exerted must be equal t its weight,
F_applied = W
= m*g
= 48.1*9.8
= 471.38 N
2) Workdone, W = F_applied*d
= 471.38*0.79
= 372.4 J
3) delta_U = +W
= 372.4
it increases
4)
F_applied = 471.38 N
W = -372.4 J
delta_U = -372.4 J
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