Orbital force when moon distance and velocity change

[vipson231]

A moon is orbiting around the planet with a constant distance of 4.0 x 10^8 with...

Homework Statement

Question/w formulas are in attachment.

I know I've been given two masses, 5.5 and 7.35 x 10^ 22 kg, and a distance of 4.0 x 10^8. But what I don't understand is the speed of 950 m/s and the 1/4 distance part. I know you use the formula F=Gm1m2/r^2 formula but what do you do with the velocity that is given and how do you find the 1/4 the distance apart?

 

[tiny-tim]

hi vipson231!

But what I don't understand is the speed of 950 m/s …

the gravitational force will be the centripetal acceleration times the mass

 

[vipson231]

I already got the answer. Thank you for the clarification though =)