Question 1
Starting an object moving, increasing its velocity, stopping it, and changing its direction of travel — what do all these things a force can do have in common?
The right answer is the one marked above.
The object's velocity changes. Starting to move is the velocity rising from 0; stopping is it falling to 0; and a change of direction is a change of velocity too, because velocity is a vector.
In chapter 2 we learned that the rate of change of velocity is acceleration. So a force is the thing that causes an acceleration — that is the central idea of this chapter.
A force does not change mass or density. Distance changes only as a consequence of the velocity changing, not directly.