Here's my problem: A 23.0-kg satellite has a circular orbit with a period of 2.35 h and a radius of 8.90×106 m around a planet of unknown mass. If the magnitude of the gravitational acceleration on the surface of the planet is 8.90 m/s2, what is the radius of the planet? I gotta say, I have no idea where to start since I don't have the mass of the planet. Any help? Pretty please? Due tonight at 10 pm EST... thanks!