If a satellite is revolving around a planet of mass M in an elliptical orbit of semi-major axis a, find the orbital speed of the satellite when it is at a distance r from the focus.
a) √(GM(2/r - 1/a))
b) √(GM(2/a - 1/r))
c) √(GM(1/r - 1/a))
d) √(GM(1/a - 1/r))
