Physics question. Please help.?

Question

A satellite orbits a planet of unknown mass in a circle of radius 2.0 x 10^7 meters. The magnitude of the gravitational force on the satellite from this planet is F=80N.

A) What is the kinetic energy of the satellite in this orbit?
B) What would F be if the orbit radius were increased to 3.0 x 10^7 meters?

Answer 1

Kinetic energy is equal to negative half of virial of forces.
http://en.wikipedia.org/wiki/Virial_theorem
Virial of the force of gravity is
Vr = F * R = -160 e+7 Nm

Answer: (a) 800 MJoules