Potential Energy of Comet-Sun System: Calculate the Answer

[moondawg]

Homework Statement

A comet of mass 1.2x10¹⁰kg moves in an ellyptical orbit around the sun. It's distance from the Sun ranges between .5 AU and 50 AU. At aphelion what is the potential energy of the comet sun system?

Homework Equations

AU=1.496x10¹¹

The Attempt at a Solution

F= ((G(1.99x10³⁰)(1.2x10¹⁰))/(7.4807x10¹²)²=28462.67N... but that seems to small of a force, what am i doing wrong??

 

[Delphi51]

You found the force, but you were asked for the energy.
Look up the formula for gravitational potential energy if you need to.

 

[housemartin]

Aphelion is point on the orbit with largest distance from the sun. Why do you plug numbers in force expression, when you need to find potential energy?