Question

part d
move the slider such that the stick figure gives the crate a quick push, enough that it starts moving. (apply the force for only a short time and then remove the force.) why does the crate travel some distance before coming to a stop?
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part e
set the friction slider to
one\ and the ice will appear again. give the crate a quick push. note that the sum of forces drops down to zero. however, the crate keeps moving. why?

Explanation:

For Part D, when the crate is pushed and starts moving, it travels some distance before stopping due to friction. Friction is a force that opposes the motion of the crate and gradually dissipates its kinetic energy. For Part E, when the friction slider is set to "none" and the crate is pushed, the sum of forces becomes zero. According to Newton's first - law of motion (the law of inertia), an object in motion will stay in motion with a constant velocity when the net force acting on it is zero. So the crate keeps moving because there is no force (such as friction) to slow it down.

Answer:

Part D: The crate travels some distance before stopping because of friction which opposes its motion and dissipates its kinetic energy.
Part E: The crate keeps moving because with no friction and a net force of zero, according to Newton's first law (law of inertia), an object in motion stays in motion with a constant velocity.