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## Homework Statement

a 2000kg lunar lander is in orbit 40km above the surface of the moon. it needs to move out to a 500km orbit in oder to link up with a mothership that will take the astronauts home. it wants the answer in joules

## Homework Equations

??E2-E1=Work done by non conservative forces

## The Attempt at a Solution

I get answers like 9.91*10^9 joules or negative 9.91*10^9

i thought that Total energy in an orbit=0 so i solved E(@40km)=mv1^2-GMm/r1=2000(v1^2-GM/40000+Rmoon)