Question

A block weighs W is held against a vertical wall by applying a horizontal force F. The minimum value of F needed to hold the block is

• A. Less than W
• B. Equal to W
• C. Greater than W
• D. Data is insufficient

Answer 1

Answer: (C)

Greater than W

Answer 2

Here applied horizontal force F acts as normal reaction. For holding the block

Force of friction = Weight of block

$f = W$ ⇒ $\mu R = W$ ⇒$\mu F = W$

⇒ $F = \frac{W}{\mu}$

As $\mu < 1$ $\therefore\mspace{6mu}\mspace{6mu}\mspace{6mu} F > W$