Jason slides a large crate down a ramp from a truck to the ground. To control th

Question

Jason slides a large crate down a ramp from a truck to the ground. To control the crate and keep it sliding at constant speed, Jason backs down the ramp in front of the crate while pushing upward on it. During its trip to the bottom, is the thermal energy created in the ramp and the crate greater than, less than, or equal to the crate's loss of gravitational potential energy? Explain. Drag the terms on the left to the appropriate blanks on the right to complete the sentences. If the crate slid down the ramp at a constant speed without Jason pushing back on it (as it could if the angle were adjusted just right) then, by conservation of energy, the increase in energy would exactly equal the loss in energy. But in fact Jason is pushing on the crate in a direction opposite its motion. Thus he is doing work on the crate, the system. So some of the loss of energy that would otherwise have gone into increasing energy is instead removed from the system, so the increase in thermal energy is actually the loss in potential energy.

Explanation / Answer

Part A : During its trip to the bottom, is the thermal energy created in the ramp and the crate greater than, less than, or equal to the crate's loss of gravitational potential energy?

Answer : It must be LESS THAN the crate's loss of gravitational potential energy and it must be less than by the amount of work Jason does pushing up on the crate.

If the crate slid down the ramp at a constant speed without Jason pushing back on it (as it could if the angle were adjusted just right) then, by conservation of energy, the increase in thermal energy would exactly equal the loss in gravitational potential energy.

But in fact Jason is pushing on the crate in a direction opposite its motion. Thus, he is doing negative work on the crate, removing energy from the system.

So some of the loss of gravitational potential energy that would otherwise have gone into increasing thermal energy is instead removed from the system, so the increase in thermal energy is actually less than the loss in potential energy.

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