Gravitation

JEE Main level, single correct, medium

144 of 223

Question 144 of 223

A rocket has to be launched from earth in such a way that it never returns. If EE is the minimum energy delivered by the rocket launcher, what should be the minimum energy that the launcher should have, if the same rocket is to be launched from the surface of the moon? Assume that the density of the earth and the moon are equal and that the earth's volume is 6464 times the volume of the moon.

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Answer: (D) E16\dfrac{E}{16}

Mearth=64Mmoon{M}_{earth}=64{M}_{moon} and Rearth=4Rmoon{R}_{earth}=4{R}_{moon}
Given: E=GMearthmRearthE=\dfrac{G{M}_{earth}m}{{R}_{earth}}
Now, for the moon,
E′=GMmmRm{E}^{'}=\dfrac{G{M}_{m}m}{{R}_{m}}
=GMearth64mRearth4=GMearthm16Rearth=E16=\dfrac{G\dfrac{{M}_{earth}}{64}m}{\dfrac{{R}_{earth}}{4}}=\dfrac{G{M}_{earth}m}{16{R}_{earth}}=\dfrac{E}{16}

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