15. What is the source of centripetal force that a planet requires to revolve around the Sun? On what factors does that force depend?

Gravitational force is the source of centripetal force that a planet requires to revolve around the Sun. It depends upon the following factors : (i) Mass of the planet and the Sun, i.e., depends on the product of the masses of the planet and the Sun. (ii) Distance between the planet and the Sun, i.e. depends on the square of distance between the planet and the Sun.