Work done:

$\overline{)\begin{array}{rcl}{\mathbf{W}}& {\mathbf{=}}& \mathbf{\u2206}\mathbf{E}\\ & {\mathbf{=}}& {\mathbf{E}}_{\mathbf{f}}\mathbf{-}{\mathbf{E}}_{\mathbf{0}}\end{array}}$

Gravitational energy, E:

$\overline{){\mathbf{E}}{\mathbf{=}}{\mathbf{-}}\frac{\mathbf{G}\mathbf{m}\mathbf{m}}{\mathbf{R}\mathbf{+}\mathbf{h}}}$

A 6000 kg lunar lander is in orbit 20 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?