Earth and Sun - Gravity problem

[ova5676]

Homework Statement

Earth is a satellite of the sun with an orbit radius of approximately 1.5 x 10^11 m.

a) What is the Sun's mass? **Answer:** 2.0 x 10^30 kg

b) If the Sun's radius is 6.96 x 10^8 m, how does the Sun's density compare with Earth's density? **Answer:** Psun = 1/4 Pearth

Homework Equations

g = G*m/r^2 and Fg = G*m1*m2/r^2

The Attempt at a Solution

a) So G*m1*m2/r^2

G*(m of the earth)*(mass of the sun)/radius^2

I put these values in but didn't get the answer?

b) I don't know how to do this one? Would I just see what fraction of the Sun's radius is the Earth's and that's similar to the density?

 

[gneill]

What things do you know about the Earth's orbit? What can you calculate?