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Question
A particle of mass 100 g is kept on the surface of a uniform sphere of mass 10 kg and radius 10 cm. Find the work to be done against the gravitational force between them to take the particle away from the sphere.
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Solution
The work done against the gravitational force to take the particle away from the sphere to infinity is equal to the difference between the potential energy of the particle at infinity and potential energy of the particle at the surface of the sphere.
\[\therefore W = 0 - \left( - \frac{G \times 10 \times 0 . 1}{1 \times 0 . 1} \right)\]
\[ = \frac{6 . 67 \times {10}^{- 11} \times 1}{1 \times 0 . 1}\]
\[ = 6 . 67 \times {10}^{- 10} J\]
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