Question

A force is acting on a body of mass $3kg$ kept on a rough horizontal surface. If a friction force of $40N$ is required to keep the body at rest under the action of this external force. Find the contact force acting on the body. (Take $g=10m/s^2$)

• A. $30N$
• B. $40N$
• C. $50N$
• D. $100N$

Answer 1

The correct option is C $50N$

Let the given problem be depicted pictorially as shown.

So, from the given condition we have,
Normal reaction force, $N=3g=30N$
Friction force, $f=40N$
$\therefore$ Contact force, $R=\sqrt{N^2+f^2}$
$\Rightarrow R=\sqrt{{30}^2+{40}^2}=50N$