A 17.0-kg satellite has a circular orbit with a period of 2.31 h and a radius of 9.10×106 m around a planet of unknown mass. If the magnitude of the gravitational acceleration on the surface of the planet is 8.10 m/s2, what is the radius of the planet?
The surface g equals G M/Rp^2. Rp is the planet radius in this case.
The orbital period P and distance R will also provide you with a value for M, using the Kepler third law in Newton's form (from your other question). With that, solve for Rp