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JEE Mains · Physics · STD 11 - Gravitation
  • JEE Mains 2025
  • Hard
  • Numerical

A satellite of mass \(\frac{M}{2}\) is revolving around earth in a circular orbit at a height of \(\frac{R}{3}\) from earth surface. The angular momentum of the satellite is \(M \sqrt{\frac{G M R}{x}}\). The value of \(x\) is ______ , where \(M\) and \(R\) are the mass and radius of earth, respectively. ( G is the gravitational constant)

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(D) 3

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\(\begin{aligned} & \text { orbital velocity } v_0=\sqrt{\frac{\mathrm{GM}}{4 \mathrm{R} / 3}}=\sqrt{\frac{3 \mathrm{GM}}{4 \mathrm{R}}} \\ & \text { Angular momentum of satellite }=\frac{\mathrm{M}}{2} \mathrm{v}_0 \frac{4 R}{3} \\ & =\frac{M}{2} \cdot \sqrt{\frac{3 \mathrm{GM}}{4 \mathrm{R}}} \cdot \frac{4 \mathrm{R}}{3} \\ & =M \sqrt{\frac{\mathrm{GMR}}{3}} \\ & x=3\end{aligned}\)
(ii) Since mass of satellite is comparable to the mass of earth.

\(\begin{aligned} & \frac{\text { G.M. } \frac{\mathrm{M}}{2}}{\left(\frac{4 \mathrm{R}}{3}\right)^2}=\frac{\mathrm{M}}{2} \omega^2 \cdot \frac{8 \mathrm{R}}{9} \\ & \omega=\sqrt{\frac{81 \mathrm{GM}}{128 \mathrm{R}^3}}\end{aligned}\)
Angular momentum of satellite about common centre of mass,
\(\begin{aligned}
& L=\frac{M}{2} \cdot\left(\frac{8 R}{9}\right)^2 \cdot \omega \\
& L=M \sqrt{\operatorname{GMR}\left(\frac{8}{81}\right)} \\
& x=\frac{81}{8} \simeq 10
\end{aligned}\)
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