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JEE Mains · Physics · STD 11 - Gravitation
  • JEE Mains 2021
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  • MCQ

The angular momentum of a planet of mass \(M\) moving around the sun in an elliptical orbit is \(\overrightarrow{ L }\). The magnitude of the areal velocity of the planet is:

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Answer & Solution

Correct Answer

(D) \(\frac{L }{2M }\)

Step-by-step Solution

Detailed explanation

For small displacement ds of the planet its area can be written as

\(d A =\frac{1}{2} rd \ell\)

\(=\frac{1}{2} r d s \sin \theta\)

A.vel \(=\frac{ d A }{ dt }=\frac{1}{2} r \sin \theta \frac{ ds }{ dt }=\frac{ Vr \sin \theta}{2}\)

\(\frac{ d A }{ dt }=\frac{1}{2} \frac{ mVr \sin \theta}{ m }=\frac{ L }{2 m }\)

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