Question

The magnitude of the normal reaction that acts on the block at the point $Q$ is

• A. 7.5 N
• B. 8.6 N
• C. 11.5 N
• D. 22.5 N

Answer 1

Answer: (A)

At point $Q$, component of weight along $PQ$ (radially outwards) is
$mg\cos 60^{\circ }$ or $\frac{mg}{2}$.
Normal reaction is radially inwards
$N-\frac{mg}{2}=\frac{m{v}^2}{R}$
or $N=\frac{mg}{2}+\frac{m{v}^2}{R}$
$=\frac{1\times 10}{2}+\frac{1\times (10{)}^2}{40}=7.5N$