Topic: Angular momentum and its conservation· Rotational Motion

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.

1. 100 days

2. 105 days

3. 115 days

4. 108 days

Doubtly Asked 30 Oct 2026 NEET UG 2025 Practice test neet Save WhatsApp Report

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Answer: 4. 108 days

Key idea: no external torque, so angular momentum $L=I\omega$ is conserved.

For a uniform sphere, $I=\tfrac25MR^2$. Mass stays the same, and with $R\to2R$, $I\to4I$. Then $\omega\to\omega/4$, so the period becomes 4 times larger:

$$T'=4\times27=108\ \text{days}$$

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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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.

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