Centrifugal Force- Finding Speed of Satellite

[kitenyos]

Homework Statement

In order for a satellite to move in a stable circular orbit of radius 6736 km at a constant speed, its centripetal acceleration must be inversely proportional to the square of the radius r of the orbit.
What is the speed of the satellite? The universal gravitational constant is 6.67259 × 10−11 N · m2/kg2 and the mass if the Earth is 5.98 × 1024 kg.
Answer in units of m/s.

r=6736

Homework Equations

fg=G(m1)(m2)/r^2
Ac=v^2/r
Mv^2/r=Fg

The Attempt at a Solution

One thing that trips me up is "its centripetal acceleration must be inversely proportional to the square of the radius r of the orbit." What does this mean? Once i know this i can figure it out.

 

[rock.freak667]

That just means that in fg=G(m1)(m2)/r^2, fg = m2a so that a=Gm1/r^2. Gm1 is constant so a is proportional to 1/r^2.