Question

A rectangular body is held at rest by pressing it against a vertical wall for which $\mu <1$. Which of the following is generally true?

• A. It will be easier to hold the body if the surfaces in contact are smooth.
• B. Pressing force required is smaller than weight $mg$ of the body.
• C. Pressing force required is greater than weight $mg$ of the body
• D. The required pressing force is independent of coefficient of friction between surfaces in contact.

Answer 1

The correct option is C Pressing force required is greater than weight $mg$ of the body



Since the block is in equilibrium,
$F=N$ ($F$: pressing force)
$mg=f_l$ ($f_l$ is limiting friction)
$mg=\mu N$
$mg=\mu F$
$F=\frac{mg}{\mu }$
$F>mg$ since $\mu <1$