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Gravitation question

2025 · 23 Jan · Shift 2 · Q75
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  5. /2025 · 23 Jan · Shift 2 · Q75

Gravitation question

2025 · 23 Jan · Shift 2 · Q75

JEE MainPhysicsGravitationNumerical+4 / −1
A satellite of mass M2\frac{M}{2}2M​ is revolving around earth in a circular orbit at a height of R3\frac{R}{3}3R​ from earth surface. The angular momentum of the satellite is MGMRx\mathrm{M} \sqrt{\frac{\mathrm{GMR}}{x}}MxGMR​​. The value of xxx is ‾\underline{\hspace{2cm}}​ , where M and R are the mass and radius of earth, respectively. ( G is the gravitational constant)
Numerical answer
View written solutionFree

Correct answer: 3

  1. Given data
  • Mass of satellite: m=M2m = \dfrac{M}{2}m=2M​
  • Radius of Earth: RRR
  • Height above Earth’s surface: h=R3h = \dfrac{R}{3}h=3R​

So, orbital radius from Earth’s center is r=R+R3=4R3r = R + \frac{R}{3} = \frac{4R}{3}r=R+3R​=34R​

  1. Speed of satellite in circular orbit

For a circular orbit, v=GMrv = \sqrt{\frac{GM}{r}}v=rGM​​

Substitute r=4R3r = \dfrac{4R}{3}r=34R​: v=GM4R/3=3GM4Rv = \sqrt{\frac{GM}{4R/3}} = \sqrt{\frac{3GM}{4R}}v=4R/3GM​​=4R3GM​​

  1. Angular momentum of the satellite

For circular motion, L=mvrL = mvrL=mvr

Substitute m=M2m = \dfrac{M}{2}m=2M​, v=GMrv = \sqrt{\dfrac{GM}{r}}v=rGM​​, and r=4R3r = \dfrac{4R}{3}r=34R​: L=M2⋅GMr⋅rL = \frac{M}{2} \cdot \sqrt{\frac{GM}{r}} \cdot rL=2M​⋅rGM​​⋅r

This becomes L=M2GMrL = \frac{M}{2}\sqrt{GMr}L=2M​GMr​

Now substitute r=4R3r = \frac{4R}{3}r=34R​: L=M2GM⋅4R3L = \frac{M}{2}\sqrt{GM\cdot \frac{4R}{3}}L=2M​GM⋅34R​​

L=M2⋅2GMR3L = \frac{M}{2}\cdot 2\sqrt{\frac{GMR}{3}}L=2M​⋅23GMR​​

L=MGMR3L = M\sqrt{\frac{GMR}{3}}L=M3GMR​​

  1. Compare with given form

Given, L=MGMRxL = M\sqrt{\frac{GMR}{x}}L=MxGMR​​

Comparing with L=MGMR3L = M\sqrt{\frac{GMR}{3}}L=M3GMR​​ we get x=3x = 3x=3

  1. Comparison with stored answer

Stored correct answer = 333

Our derived answer also gives x=3x = 3x=3.

Hence, the answer agrees with the stored correct answer.

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