Question

A block $W$ is held against a vertical wall by applying a horizontal force $F$. The minimum value of $F$ needed to hold the block is if $\mu <1$

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

Answer 1

The correct option is C Greater than $W$

Its the upward friction which holds the mass from falling downward as we know that the maximum value of friction is $\mu N$ where $N$ is normal reaction by Wall which is equal to Horizontal force F because horizontal force is balanced as no motion in horizontal direction.

No horizontal motion

$\Rightarrow N-F=0$

$\Rightarrow N=F$

Now to hold the weight the friction shoud have $\mu N\ge W$

put $N=F$ we get $\mu F\ge W$ or $F\ge \frac{W}{\mu }$

as$\mu <1$ so $F>W$.

Option c is correct.