gravitational potential energy

[ACLerok]

Find U, the gravitational potential energy of the object at a distance R from the center of the planet, with the gravitational potential energy taken to be zero when the object is infinitely far away from the planet. Express your answer in terms of R, m, M, and G, the universal gravitational constant.

[FZ+]

Pretty straightforward.

Write out the equation for gravitational force.

Integrate wrt distance, putting in correct limits.