Question

Find the minimum value of coefficient of friction between the $4kg$ block and the surface for the system to be at rest for the figure shown.

• A. $0.4$
• B. $0.5$
• C. $0.6$
• D. $0.75$

Answer 1

The correct option is D $0.75$

The minimum value of coefficient of friction between the block and surface will be given at the limiting friction condition.

Let the coefficient of friction between the block and the surface be ${\mu }_s$
So, from the FBDs of the blocks we get
$T=3g$
$T=f={\mu }_{s}N$
and, $N=4g$
from the above equations we have
$3g={\mu }_s\left(4g\right)$
$\Rightarrow {\mu }_s=\frac{3}{4}=0.75$