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Gravitation question

2021 · 17 Mar · Shift 2 · Q59
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  5. /2021 · 17 Mar · Shift 2 · Q59

Gravitation question

2021 · 17 Mar · Shift 2 · Q59

JEE MainPhysicsGravitationMCQ+4 / −1
A geostationary satellite is orbiting around an arbitrary planet 'P' at a height of 11R above the surface of 'P', R being the radius of 'P'. The time period of another satellite in hours at a height of 2R from the surface of 'P' is ‾\underline{\hspace{2cm}}​. 'P' has the time period of 24 hours.
  1. A
    3
  2. B
    5
  3. C
    626\sqrt 262​
  4. D
    62{6 \over {\sqrt 2 }}2​6​
View written solutionFree

Correct answer: A

  1. Use the geostationary condition

For a geostationary satellite, the orbital time period equals the rotation period of the planet: T1=24 hT_1 = 24\text{ h}T1​=24 h

It is given that this satellite is at a height of 11R11R11R above the surface.

So its distance from the center of the planet is: r1=R+11R=12Rr_1 = R + 11R = 12Rr1​=R+11R=12R

  1. Find the radius of the second satellite's orbit

The second satellite is at a height of 2R2R2R above the surface, so: r2=R+2R=3Rr_2 = R + 2R = 3Rr2​=R+2R=3R

  1. Apply Kepler's third law for satellites around the same planet

For satellites orbiting the same planet, T2∝r3T^2 \propto r^3T2∝r3

Hence, (T2T1)2=(r2r1)3\left(\frac{T_2}{T_1}\right)^2 = \left(\frac{r_2}{r_1}\right)^3(T1​T2​​)2=(r1​r2​​)3

Substitute the values: (T224)2=(3R12R)3\left(\frac{T_2}{24}\right)^2 = \left(\frac{3R}{12R}\right)^3(24T2​​)2=(12R3R​)3 (T224)2=(14)3=164\left(\frac{T_2}{24}\right)^2 = \left(\frac{1}{4}\right)^3 = \frac{1}{64}(24T2​​)2=(41​)3=641​

Taking square root, T224=18\frac{T_2}{24} = \frac{1}{8}24T2​​=81​ T2=24×18=3 hT_2 = 24 \times \frac{1}{8} = 3\text{ h}T2​=24×81​=3 h

  1. Match with the options

Thus, the time period of the second satellite is: 3 h\boxed{3\text{ h}}3 h​

So the correct option is A.

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