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**Gravitation Potential Energy Problem of WHY?**

## Homework Statement

Energy is required to move a 1540 kg mass from the Earth’s surface to an altitude 3.12 times the Earth’s radius RE. What amount of energy is required to accomplish this move? The acceleration of gravity is 9.8 m/[itex]s^{2}[/itex].

## Homework Equations

ΔU = G

*m*[itex]M_{E}[/itex]/([itex]\frac{1}{R}[/itex] - [itex]\frac{1}{4.12R}[/itex])

## The Attempt at a Solution

I know the equation and you just plug it in. But I am having problem of understanding the equation itself. I don't want to just plug numbers in unless I know what I'm doing.

So what I'm confused about is... why do I need the potential energy of the earth? Why can I not just use U = G

*m*[itex]M_{E}[/itex]/4.12R??