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JEE Main 20137 April
Exam
JEE Main
Year
2013
Date
7 April
Subject
Physics
Chapter
Gravitation

JEE Main 2013 · 7 April · Physics · Gravitation

What is the minimum energy required to launch a satellite of mass m...

What is the minimum energy required to launch a satellite of mass m\text{m} from the surface of a planet of mass M\text{M} and radius R\text{R} in a circular orbit at an altitude of 2R\text{2R}?

Options

  1. AGmM2R\dfrac{\text{GmM}}{2 \text{R}}
  2. BGmM3R\dfrac{\text{GmM}}{3 \text{R}}
  3. C5GmM6R\dfrac{5 \text{GmM}}{6 \text{R}}
  4. D2GmM3R\dfrac{2 \text{GmM}}{3 \text{R}}

Correct answer

C. 5GmM6R\dfrac{5 \text{GmM}}{6 \text{R}}

Step-by-step solution

As we know,
Gravitational potential cnergy =−GMmr= \dfrac{- GMm}{r}
and orbital velocity, v0=GM/R+h{v}_{0} = \sqrt{GM / R + h}
Ef=12mv02−GMm3R=12mGM3R−GMm3R{E}_{f} = \dfrac{1}{2}{mv}_{0}^{2} - \dfrac{GMm}{3R} = \dfrac{1}{2}m\dfrac{GM}{3R} - \dfrac{GMm}{3R}
=GMm3R(12−1)=−GMm6R= \dfrac{GMm}{3R}\left(\dfrac{1}{2} - 1\right) = \dfrac{- GMm}{6R}
Ei=−GMmR+K{E}_{i} = \dfrac{- GMm}{R} + K
Ei=Ef{E}_{i} = {E}_{f}
Therefore minimum required energy,
K=5GMm6RK = \dfrac{5GMm}{6R}
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