Question

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

• A. $30\text{N}$
• B. $40\text{N}$
• C. $50\text{N}$
• D. $100\text{N}$

Answer 1

The correct option is C $50\text{N}$

Net Contact force will be normal on the block upward and frictional force opposing the tendency of relative motion of $\text{40}N$
$=F=\sqrt{N^2+f^2}=\sqrt{{30}^2+{40}^2}$
$=50\text{N}$