Question:
What is the source of centripetal force that a planet requires to revolve around the sun ? On what factors does that force depend?
Solution:
The source of centripetal force that a planet requires to revolve around the sun is the gravitational force between the sun and the planet. Thus,
$\mathrm{F}=\frac{\mathrm{GM}_{s} \mathrm{M}_{p}}{r^{2}}$
where $m$ is the mass of the sun, is the mass of the planet and $r$ is the distance between the sun and the planet.
Thus, the force depends upon
1. the mass of the sun,
2. the mass of the planet and
3. the distance between the sun and the planet.