# Homework Help: Ratio Problem Dealing with Radius and Centripetal Acceleration

1. Mar 1, 2012

### PeachBanana

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

Two identical satellites orbit the earth in stable orbits. One satellite orbits with a speed v at a distance r from the center of the earth. The second satellite travels at a speed that is less than v . At what distance from the center of the earth does the second satellite orbit?

2. Relevant equations
a = (v)^2/r
F = m/a
F = G (M * m )/ r^2

3. The attempt at a solution

I'm really confused on how to manipulate these equations.

Ultimately, I need to find an equation that relates "r" to "v."
r = a * v^2
So if the second satellite is moving slower doesn't that mean "r" has to be bigger? This makes me think of one of Kepler's Laws.

2. Mar 1, 2012

### genericusrnme

That should read F=ma or a=F/m

What does satellites orbit the earth in stable orbits tell you about the system?
I'm not sure you understand what you're actually doing when you're working with these equations

3. Mar 1, 2012

### PeachBanana

Wow. That was really careless of me. When it comes to problems like these, I don't understand how to do them well. Stable orbits = equal gravitational force?

4. Mar 1, 2012

### genericusrnme

What should the gravitational force equal?

What does it mean if the orbit is stable?