Many communication satellites are placed in a circular orbit around the earth at a radius where the period (the time to go around the earth once) is 24 hours. if the satellite is above some point on the equator, it stays above that point as the earth rotates, so that as viewed from the rotating earth the satellite appears to be motionless. that is why you see dish antennas pointing at a "fixed" point in space. calculate the radius of the orbit of such a "synchronous" satellite. show your work on paper, starting from the momentum principle (don't just quote some canned formula).