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MHT CET 2019 (2 May, Shift 2) · Satellite Energy & Weightlessness

Satellite Energy & Weightlessness question from MHT CET 2019 (2 May, Shift 2)

Q27MHT CET 2019 · 2 MAY · SHIFT 2Medium

Satellite Energy & Weightlessness

What is the minimum energy required to launch a satellite of mass ' mm ' from the surface of the earth of mass ' MM ' and radius ' RR ' at an altitude 2R2R?

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Answer: (b)

  1. Energy just to raise it to altitude 2R2R (r=3Rr = 3R): ΔU=GMm(1R−13R)=2GMm3R\Delta U = GMm\left(\frac{1}{R} - \frac{1}{3R}\right) = \frac{2GMm}{3R}.
  2. If it must also orbit there, add K=GMm6RK = \frac{GMm}{6R}, giving 5GMm6R\frac{5GMm}{6R}.
  3. Taking 'launch to an altitude 2R2R' as only raising it, the answer is (b) 2GMm3R\frac{2GMm}{3R}.
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