PHYSICS · Multi-part · A Level · Physics · Mechanics and materials · Mechanics and materials
Problem
A 2.0kg block rests on a horizontal workbench. The coefficient of static friction between the block and the bench is 0.45 and the coefficient of kinetic friction is 0.35. Beginning at t=0, a student pushes horizontally on the block; the magnitude of the push is changed several times as shown in the table below.
Time interval (s)
0−2
2−4
4−6
6−8
Push magnitude (N)
5
8
11
18
Assume the push always acts toward the right.
(a) Before the block begins to slide, describe qualitatively how the friction force exerted by the bench responds to changes in the student’s push. Include the direction and relative magnitude of the friction force for each time interval.
(b) For each time interval, determine whether the block remains at rest or moves. Justify your answer with appropriate numerical reasoning.
(c) During any interval in which the block does not move, state the magnitude of the friction force exerted by the bench and explain how that value is established.
(d) The student repeats the experiment using a block with the same mass but a larger contact area. Predict and explain whether the push required to make this larger block begin to slide is greater than, less than, or equal to the push required in the original experiment.