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Gravitation question

2023 · 29 Jan · Shift 2 · Q56
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  5. /2023 · 29 Jan · Shift 2 · Q56

Gravitation question

2023 · 29 Jan · Shift 2 · Q56

JEE MainPhysicsGravitationMCQ+4 / −1
The time period of a satellite of earth is 24 hours. If the separation between the earth and the satellite is decreased to one fourth of the previous value, then its new time period will become.
  1. A
    12 hours
  2. B
    3 hours
  3. C
    6 hours
  4. D
    4 hours
View written solutionFree

Correct answer: B

  1. For a satellite revolving around Earth, Kepler’s third law gives T2∝r3T^2 \propto r^3T2∝r3 where TTT is the time period and rrr is the distance (orbital radius) from the center of Earth.

  2. Initially, T1=24 hoursT_1 = 24\text{ hours}T1​=24 hours Let the initial separation be r1r_1r1​.

  3. The new separation is decreased to one fourth of the previous value: r2=r14r_2 = \frac{r_1}{4}r2​=4r1​​

  4. Using (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 we get (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​

  5. Taking square root, T224=18\frac{T_2}{24} = \frac{1}{8}24T2​​=81​ so T2=24×18=3 hoursT_2 = 24 \times \frac{1}{8} = 3\text{ hours}T2​=24×81​=3 hours

  6. Therefore, the new time period is 3 hours\boxed{3\text{ hours}}3 hours​

  7. Checking options:

    • A: 121212 hours ❌
    • B: 333 hours ✅
    • C: 666 hours ❌
    • D: 444 hours ❌
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