4-2.Friction
medium

The coefficient of static friction between a wooden block of mass $0.5\, kg$ and a vertical rough wall is $0.2$ The magnitude of horizontal force that should be applied on the block to keep it adhere to the wall will be $N$ $\left[ g =10\, ms ^{-2}\right]$

A

$25$

B

$30$

C

$30$

D

$20$

(JEE MAIN-2021)

Solution

$F.B.D.$ of the block is shown in the diagram

Since block is at rest therefore

$fr – mg =0$ $……..(1)$

$F- N =0$  $……….(2)$

$fr \leq \mu N$

In limiting case

$fr =\mu N =\mu F$  $……..(3)$

Using eq. $(1)$ and $(3)$

$\therefore \mu F = mg$

$\Rightarrow F=\frac{0.5 \times 10}{0.2}=25 N$

Standard 11
Physics

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