Question

A block of mass $0.1\text{kg}$ is held against a wall by applying a horizontal force of $5\text{N}$ on the block. If the coefficient of friction between the block and the wall is $0.5$, the magnitude of the friction force acting on the block is

• A. $2.5\text{N}$
• B. $0.98\text{N}$
• C. $4.9\text{N}$
• D. $0.49\text{N}$

Answer 1

The correct option is B $0.98\text{N}$

From FBD

$R=5\text{N}$
To find the limiting friction
$f_s={\mu }_{s}R$
$=0.5\times 5=2.5\text{N}$
$\therefore$ External force $\left(mg\right)=0.98N<2.5N$
The static frictional force $\left(f_s\right)=0.98\text{N}$