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:

  1. 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

$$ \begin{aligned} N-\frac{m g}{2} & =\frac{m v^{2}}{R} \\ \text { or } \quad N & =\frac{m g}{2}+\frac{m v^{2}}{R} \\ & =\frac{1 \times 10}{2}+\frac{1 \times(10)^{2}}{40}=7.5 N \end{aligned} $$



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