The Box.........

Question

You lift a 64.00-kg box from the floor onto a shelf 1.50m above the floor.

If you lift the box with a constant speed, what is the magnitude of the force you exert on the box? Is it upward or downward?

Answer 1

Hello Andrew. If you are lifting the box with a constant speed then that means the net force on it must be zero. This means that the upward force you apply to it is exactly canceled out by the downward force of gravity. The force exerted by gravity is F = -mg where the negative sign indicates a downward force. So then the force you exert on the box is F = mg (note that it is now positive, indicating an upward force).

m = 64.00 kg

g = 9.8 m/s²

F = (64.00 kg)(9.8 m/s²) = 630 Newtons (I rounded to two significant figures because 9.8 has only two significant figures).

So the final answer would be 630 Newtons upward.