# Planetary motion the mass of the sun

#### 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 ???

Related Introductory Physics Homework News on Phys.org

#### Janus

Staff Emeritus
Science Advisor
Gold Member
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.)

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving