Question
Answer the following:
Comets move around the sun in highly elliptical orbits. The gravitational force on the comet due to the sun is not normal to the comet’s velocity in general. Yet the work done by the gravitational force over every complete orbit of the comet is zero. Why?

Answer

The gravitational force is a conservative force, hence, work done by the gravitational force over one complete (closed) orbit of comet is zero.

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