Rotational MotionMedium

Question

The Sun rotates around its centre once in 27 days. What will be the period of revolution if the Sun were to expand to twice its present radius without any external influence? Assume the Sun to be a sphere of uniform density.

Options

A.100 days
B.105 days
C.115 days
D.108 days

Solution

Assuming the Sun to be a solid sphere, $I = \frac{2}{5}mR^{2}$

Using conservation of angular momentum, $l^{'}\omega^{'} = l\omega$

$$\begin{matrix} & \ \Rightarrow \frac{2}{5}m(2R)^{2} \times \frac{2\pi}{T^{'}} = \frac{2}{5}mR^{2} \times \frac{2\pi}{T} \\ & \ \Rightarrow T^{'} = 4T = 4 \times 27 = 108\text{~}\text{days}\text{~} \end{matrix}$$

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