Gujarat BoardEnglish MediumSTD 11 SciencePhysicsModel Paper 52 Marks
Question
Calculate the energy required to move a body of mass $m$ from an orbit of radius $2 R$ to $3 R$.
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Answer
Gravitational PE of mass m in orbit of radius $R=U=-\frac{G M m}{R}$ $ \begin{aligned} & \therefore U_i=\frac{G M m}{2 R} \\ & U_f=-\frac{G M m}{3 R} \end{aligned} $ Energy required = Potential energy of the Earth(mass system when mass is at distance 3R) - Potential energy of the Earth (mass system when mass is at distance 2R) $ \begin{aligned} & \Delta U=U_f-U_i=G M m\left[\frac{1}{3}-\frac{1}{2}\right] \\ & =\frac{G M m}{6 R} \end{aligned} $
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