# Planetary motion the mass of the sun

1. Oct 29, 2007

### prospec

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

Derive the equation using Newton's Law of gravitation and the equation for circular motion.

2. Relevant equations

V = $$\sqrt{\stackrel{GM}{r}}$$

Where G is the universal gravitational constant, M is the mass of the central body and r is the radius of the orbit

3. The attempt at a solution

F= GM1*m2/r2

F= GMp*Ms/r2

Fc= MpV2/r

F=FC

GMpMS/r2 = mpV2/r

I'm not sure how to derive this equation ???

2. Oct 29, 2007

### Janus

Staff Emeritus
Your heading in the right direction, now all you do is re-arrange the last equation until you've solved for V. (hint: some of the variables at least partially cancel out.)