Circular Motion (ratio of velocities)

[Qualenal]

Homework Statement

Two small planets are moving in circular orbits around the same star. If the radius of the orbit of planet A is 4 times the radius of the orbit of planet B, find the ratio of their speeds vA/vB.

Homework Equations

Not really sure but
v=omega*r
a(centripetal)=v^2/r
UCM T=2*pi*r/v

The Attempt at a Solution

I honestly have no idea how to do this problem. I know the answer is .5 I just want to know how to get there!

 

[gneill]

Homework Statement

Two small planets are moving in circular orbits around the same star. If the radius of the orbit of planet A is 4 times the radius of the orbit of planet B, find the ratio of their speeds vA/vB.

Homework Equations

Not really sure but
v=omega*r
a(centripetal)=v^2/r
UCM T=2*pi*r/v

The Attempt at a Solution

I honestly have no idea how to do this problem. I know the answer is .5 I just want to know how to get there!

Have a look at Kepler's third law. It may give you a starting point.