The Moon orbits the Earth at an average distance of 3.84 105 km with an orbital period of 0.07481 yr. Neptune, which is one of the satellites of the Sun, orbits its parent at an average distance of 4.50 109 km with an orbital period of 164.8 yr. (a)
Use the above information to find the orbital speeds of the Moon around the Earth and of Neptune around the Sun.
vMoon
= m/s
vNeptune
= m/s
(b)
What is the expression for the mass M of the parent in terms of the orbital speed v of the satellite, the orbital radius R of the satellite and the gravitational constant G? (Do not substitute numerical values; use variables only.)
M =

Consider Newton's Universal Law of Gravitation. What supplies the centripetal force needed for the satellite to go around its parent?
(c)
Now use your answers from parts (a) and (b) to find the ratio of the mass of the Sun to that of the Earth.