Question

A block has weight $W$ and it is wall held against a vertical wall by applying a horizontal force $F$. The minimum value of $F$ is

• A. less then $W$
• B. equal to $W$
• C. greater than $W$
• D. not settled by the data.

Answer 1

Answer: (C)

The mass is held up by the force of static friction.
$f=W$ and $f\le \mu N$ or $f\le \mu F$
$\Rightarrow W\le \mu F$ or $F_{\min }=\frac{W}{\mu }$
$\ge \mu$ is always less than $1,\frac{W}{\mu }>W$ or $F_{\min }>W$