申論題

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

(b) (10 points) The ratio between the tidal force exerted by the Moon to that exerted by the Sun is 7 to 3. Estimate the ratio of the average density of the Moon to that of the Sun.
 [State clear the assumptions you made and the extra information (if any) that you used.]