Answer:
a. Velocity
Explanation:
The slope of the tangent line on a position-time graph is the instantaneous velocity.
This is easily explained saying that the frictional force between the books and the paper isn't big enough to produce a displacement in the books. The displacement in the books doesn't happen because the frictional force between the books and the surface they are standing on is bigger than the paper's one.
4. 1 and 2 only.
1. the downward force is the force of gravity.
<span>2. The upward force exerted is the Normal reaction from the floor.</span>
The object will not be able to accelerate perpendicular to direction of motion
