Question

A block pressed against the vertical wall is in equilibrium. The minimum coefficient of friction is:

• A. $0.4$
• B. $0.2$
• C. $0.5$
• D. none of these

Answer 1

Answer: (C)

Here net driving force

$=mg-\frac{mg}{2}=\frac{mg}{2}$ down ward

Hence friction will act upward and its magnitude should be $f=\frac{mg}{2}$

If the block ‘m’ is stationary the friction between $m$ and the wall should be static

$f\le f_{\text{lim}}$

$\frac{mg}{2}\le \mu \cdot N$

$\Rightarrow \frac{mg}{2}\le \mu \left(mg\right)$

$\Rightarrow \mu =\frac{1}{2}$