Determine the Altitude of a Satellite above Earth Given it's Constant Speed

[PhysicsJunkie]

Homework Statement

A remote-sensing satellite travels in a circular orbit at a constant speed of 8.2 x 10^3 m/s. Determing the altitude in kilometres of the satellite above Earth's surface.

Homework Equations

Fc = FG

The Attempt at a Solution

mv^2/r = GMm/r^2
v^2 = GM/r
r = GM/v^2
r = (6.67 x 10^-11 * 5.98 x 10^24)/(8.2 x 10^3)^2
r = 5931975 m - radius of Earth (6.38 x 10^6 m)
r = NEGATIVE NUMBER

Why am I getting a negative number? Is there a mistake in my conversions or am I completely off as to how to solve this? Any help will be greatly appreciated. :)

 

[LowlyPion]

Using μ = G*M ≈ 400,000 (if you keep things in km), I get V²= 400,000/(8.2)² = 5948 km.

Maybe it's a fast Earth worm?