Question

A block of mass $3\text{kg}$ is placed on a rough horizontal surface $({\mu }_s=0.4)$. A force of $8.7\text{N}$ is applied on the block. If $g=10{\text{ms}}^{-2}$, then the force of friction between the block and floor is

• A. $8.7\text{N}$
• B. $12\text{N}$
• C. $10\text{N}$
• D. Zero

Answer 1

The correct option is A $8.7\text{N}$

Limiting friction $f_{max}={\mu }_{s}mg=0.4\times 3\times 10\text{N}=12\text{N}$
Since the applied force is less than $12\text{N}$, the force of friction is equal to the applied force.
$\therefore f=8.7\text{N}$