GravitationMedium
Question
The amount of work done to raise a mass ' $m$ ' from the surface of the Earth to a height equal to the radius of the Earth ' $R$ ' will be
Options
A.$2mgR$
B.$mg\frac{R}{4}$
C.$mgR$
D.$mg\frac{R}{2}$
Solution
Sol. [Key Concept: Gravitation — work to raise mass to height h=R] W.D. $= U_{2} - U_{1}$
$$\begin{matrix} & \ = - \frac{GMm}{R + R} - \left( \frac{- GMm}{R} \right) \\ & \ = - \frac{GMm}{2R} + \frac{GMm}{R} \\ & \ = \frac{GMm}{2R} = \frac{mgR}{2} \end{matrix}$$
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