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## Homework Statement

a satellite of mass 100kg travels in a circular orbit around the earth, how much energy is required to move it to an altitude of 400km?

## Homework Equations

E

_{k}=1/2*mv

^{2}

U= -G(m

_{1}m

_{2})/r

## The Attempt at a Solution

i took the satellite as the system, so as it moves to the altitude of 400km, gravity is constantly doing negative work on it, so the energy given to the satellite on the ground must be equal to the amount of energy drained by gravity's work, so it reaches the altitude.

further more, the satellite is in an orbit, so it has kinetic energy too, thus its total amount of energy needed to lift it to 400 km will be the sum of kinetic and the energy used by gravity.

for the eqn, i would write : E

_{sum}=1/2*mv

^{2}+-G(m

_{1}m

_{2})/r

however the eqn suggests the energy of the satellite is E

_{k}-U???

is this right? so the amount of energy required to lift the sattlite is E

_{k}-U????

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