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**1. Homework Statement**

A 6000 kg lunar lander is in orbit 10 km above the surface of the moon. It needs to move out to a 100 km-high orbit in order to link up with the mother ship that will take the astronauts home.

How much work must the thrusters do?

**2. Homework Equations**

U_s = -GMm/r

F_g = GMm/r^2

**3. The Attempt at a Solution**

I tried to calculate the difference in force between the two orbits and then calculate the change in energy to get the work, but I've had no luck.