# Work required to lift object from earth's surface to circular orbit

## Homework Statement

How much work must be done by a rocket engine to lift a 1000kg payload from rest on the earth's surface to a circular orbit of radius 2Re (2 times the radius of the earth)?

Eg = -GmM/r
Ek = GmM/2r

## The Attempt at a Solution

I know ΔE = W
I know that the energies are the following:
Initial E {0 + Eg} <-- assuming its at rest
Final E {0 + Eg} <-- when it has reached this distance.

However, I don't know how I am going to solve this out, or whether or not what I did was correct...

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ideasrule
Homework Helper
Initial E {0 + Eg} <-- assuming its at rest
This is correct.
Final E {0 + Eg} <-- when it has reached this distance.
This is not. Kinetic energy can't be zero, or else the satellite would plummet to the ground instead of orbiting.

Once you figure out the final and initial energies, work done is just the difference between the two, as you've noted in your first equation.

HallsofIvy