A typical GPS (Global Positioning System) satellite orbits at an altitude of 2.0e7 m. Find the orbital speed of such a satellite in km/s. So we know: Mass of the earth (M) =5.97e24 Radius of the earth (R) =6.37e6 G is constant =6.67e-11 I used the equation: Final velocity=square root (2GM/R) square root ((2*6.67e-11*5.97e24)/(6.37e6+2.0e7)) And dividing the answer by 1000 to obtain km/s I get 5.50km/s. The answer is 3.9km/s.... I think my error may be related to adding the altitude to the radius of the earth at the bottom of the equation, but I'm not sure. Thanks guys!