申論題

(3) (20 points)
 The Sun and the Moon exert tidal force on the Earth.

(a) (10 points) Consider the Earth as a sphere of mass with radius R_E. Derive, with the help of a diagram, the tidal force exerted by the Moon on the Earth's surface.
 (Hint: assume the distance between the Moon and the Earth deM is much larger than R_E.]