During the Apollo lunar explorations of the late 1960s and early 1970s, the main section of the spaceship remained in orbit about the Moon with one astronaut in it while the other two astronauts descended to the surface in the landing module. Assume the mass of this section is 5000 kg.

A: If the main section orbited about 50 mi above the lunar surface, determine the gravitational potential energy. U = __________ J