Work Power and Energy 3 Question 4
4. 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) $22.5 N$
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Answer:
Correct Answer: 4. (a)
Solution:
- At point $Q$, component of weight along $P Q$ (radially outwards) is $m g \cos 60^{\circ}$ or $\frac{m g}{2}$.
Normal reaction is radially inwards
$$ \begin{aligned} N-\frac{m g}{2} & =\frac{m v^{2}}{R} \\ \text { or } \quad N & =\frac{m g}{2}+\frac{m v^{2}}{R} \\ & =\frac{1 \times 10}{2}+\frac{1 \times(10)^{2}}{40}=7.5 N \end{aligned} $$
