# Orbits and Potential Energy

#### HeatherH

Hi!

I really don't even understand what this problem is talking about! If someone could just point me in the right direction, I would appreciate it!

A satellite is placed in a noncircular orbit about the Earth. The farthest point of its orbit (apogee ) is 4 Earth radii from the center of the Earth, while its nearest point (perigee ) is 2 Earth radii from the Earth's center. If we define the gravitational potential energy U to be zero for an infinite separation of Earth and satellite, find the ratio U perigee/U apogee .

Thanks!

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#### dextercioby

Science Advisor
Homework Helper
The first sentence doesn't sound good. I mean are any words or concepts unclear in the problem's text...?

Daniel.

#### Doc Al

Mentor
HeatherH said:
I really don't even understand what this problem is talking about!
Start by looking up (or, better yet, deriving) the general expression for gravitational potential energy, which comes from Newton's law of gravity. Hint: U depends on the masses and the distance from the center of the earth.

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