# Finding Density of a Planet Using Period of Orbit

1. Oct 16, 2009

### surferdud3

1. The problem statement, all variables and given/known data

A satellite is in a circular orbit very close to the surface of a spherical planet. The period of the orbit is T = 1.78 hours.
What is density (mass/volume) of the planet? Assume that the planet has a uniform density.

2. Relevant equations

T$$^{2}$$=4*PI^2*r^3/G*M
Density = Mass/Volume
Volume of Sphere = 4/3*PI*r^2

3. The attempt at a solution
I converted T into seconds, which I get 6408 seconds,

I have tried to solve for a single variable, but when I put it back into the equation, everything cancels out......

What should I do, I'm just super confused..... :(

2. Oct 16, 2009

### rock.freak667

So we have

$$T^2=\frac{4\pi^2 r^3}{GM}$$

and we know $V=\frac{4}{3}\pi r^3$

So if we divide the equation with T2 by 3, can we somehow factor out (4/3)πr3?