Q 11-06-005NEETNEET 2025Top questionEasy
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.
Answer: (D) $108$ days
With no external torque, angular momentum is conserved: $I\omega = \text{constant}$.
For a uniform sphere, $I = \dfrac{2}{5}MR^2$, so $R^2\omega$ is constant and $T \propto R^2$.
$$T_2 = T_1\left(\frac{R_2}{R_1}\right)^2 = 27 \times 4 = 108\ \text{days}$$
Solution by Sreeraj P, M.Sc Physics