Determining the satellite's altitude above the surface of the Earth

[torquey123]

Homework Statement

A satellite moves in a circular orbit around the Earth at a speed of 5.1km/s.
Determine the satellite's altitude above the suface of the Earth. Assume the Earth is a homogenous sphere of radius Rearth= 6370km, and mass Mearth=5.98x10^24 kg. You will need G=6.67259x10^(-11) Nm^2/kg^2. Answer in units of km

Homework Equations

v^2=(G*Mass of earth)/(radius)

The Attempt at a Solution

(5100 km/s)^2 = (6.67259x10^(-11))(5.98x10^(24))/r

26010000r=3.990190282e14

r= 15340985.32 - 6370000= 8970985.321m = 8970.985321km

i think its wrong, but i don't know where i made the mistake..

 

[torquey123]

never mind...i figured it out when i typed it out...i didnt convert back to km