Question

A block is placed on a rough floor and a horizontal external force F is applied on it. The force of friction f by the floor on the block is measured for different values of F and a graph is plotted between them. (taking f on Y and F on X axis)

• A. (a)The graph is a straight line of slope
• B. The graph is a straight line parallel to the F-axis
• C. The graph is a straight line of slope for small F and a straight line parallel to the F-axis for large F
• D. There is a small kink on the graph

Answer 1

Answer: (C), (D)

The correct options are
C

The graph is a straight line of slope for small F and a straight line parallel to the F-axis for large F

D

There is a small kink on the graph

Limiting friction = ${\mu }_s$ mg

So till F $\le$ $f_r$

F = fr

So straight line at angle ${45}^{\circ }$

After that even if Force F increases the value of friction will be fixed at ${\mu }_K$ mg

So straight line also ${\mu }_K$ < ${\mu }_s$

So there will be kink.