A crate is pushed horizotally along the floor.?

Question

Describe the changes in kinetic energy and in gravitational potential energy.

Answer 1

Kinetic energy is a function of the square of the speed, if it is pushed at a constant rate, then that kinetic energy does not change.
Since the crate is pushed horizontally, not gaining and not losing any altitude, then the gravitational potential energy remains constant.

Answer 2

Gravitional potential energy only changes with changes in HEIGHT. So it does not change.

Kinetic energy is the change is TOTAL MOMENTUM, we assume mass is constant so the simplified view is the change in KE == change in force (how much you pushed the crate... (on a more detailed analysis one would argue there is also non-friction heating, as you are radiating some heat into the crate too, though this is generally not what the question is asking)

Answer 3

No change in gravitational (potential) energy since it is moving horizontally (m.g.h is constant).

Kinetic energy is 0.5m.v.v (half m v squared!), so this changes as crate is moved. When the crate stops the KE is lost. KE can be lost, whereas momentum (m.v) must be conserved. The KE is lost as heat and sound (both due to friction of crate on the floor).