Q 11-07-029NEETJEE MainMedium
A satellite of mass $m$ is moved from a circular orbit of radius $2R$ to one of radius $4R$ around the Earth (mass $M$, radius $R$). The work required is
Answer: (A) $\dfrac{GMm}{8R}$
Concept. Orbital energy $E = -\dfrac{GMm}{2r}$; work $=$ change in $E$.
Step 1. Work. $-\dfrac{GMm}{8R} + \dfrac{GMm}{4R} = \dfrac{GMm}{8R}$.
Answer. $\dfrac{GMm}{8R}$ (Option A).
Solution by Sreeraj P, M.Sc Physics