Question

Two smooth blocks are placed at a smooth corner as shown in figure. Both the blocks are having mass $m$. We apply a force $F$ on the small block $m$. Block $A$ presses block $B$ in the normal direction, due to which pressing force on vertical wall will increase, and pressing force on the horizontal wall decreases, as we increases $F\left(\theta=37^{\circ}\right.$ with horizontal).

As soon as the pressing force on the horizontal wall by block $B$ becomes zero, it will lose contact with ground. If the value of $F$ further increases, block $B$ will accelerate in the upward direction and simultaneously block $A$ will move towards right.
If both the blocks are stationary, the force exerted by ground on block $A$ is

• A. $m g+\frac{3 F}{4}$
• B. $m g-\frac{3 F}{4}$
• C. $m g+\frac{4 \bar{F}}{3}$
• D. $m g-\frac{4 F}{3}$

Answer 1

Answer: (C)

If both the blocks are stationary.
Balancing forces along $x$-direction
$F =N \sin \theta$
$\Rightarrow N =F / \sin \theta$
Balancing forces along $y$-direction.
$N_{y} =m g+ N \cos \theta$
$=m g+\left(\frac{F}{\sin \theta}\right) \cos \theta=m g+F \cot \theta$
$N_{y} =m g+\frac{4 F}{3}$