Force + Acceleration?

Question

If a woman who has been pushing a box to accelerate it, suddenly stops applying a horizontal force to the box, then the box will: increase its speed for a while and then start slowing to a stop, continue at a constant speed, continue moving at a constant speed for a while and then slow to a stop, immediately start slowing to a stop, immediately come to a stop.

Since the force would become negative, but the mass would stay the same, I thought that the car would immediately start slowing to a stop, but that is not the correct answer.

Any ideas?

Answer 1

It does immediately start slowing, why do you say that is not correct?
If this is one of those hypothetical cases where there is no friction then then it will continue at a constant speed, but if one is using imaginary conditions, one has to say so.

Answer 2

The moment she stops pushing the box, the acceleration becomes negative since there is always a frictional force opposing the forward movement. So, the box will immediately start slowing to a stop.

If the frictional force is neglected, then the acceleration becomes zero and the box would continue with a constant velocity.

Answer 3

This depends whether or not you are including any other external forces in this problem such as friction. If you are, then the box would immediately begin to slow. If not, then the box would continue at a constant speed.

Answer 4

You haven't told us the whole story. You can be pushing a box to accelerate it WITHOUT FRICTION. In that case the box will continue at whatever speed it was at when she let off pushing. Also, she could be accelerating the box in a direction opposite to its velocity, and stop accelerating when V=0. In that case the box would stop at the instant she stopped pushing

If friction IS present, then you are right. (Providing, once again, that V≠0 when the pushing stops)

Answer 5

it moves at constant speed, then slows down