2 Jupiter sized planets are released [tex] 1.0 X 10^11 [/tex] m What are their speeds as they crash together?(adsbygoogle = window.adsbygoogle || []).push({});

I decided to try to do this problem with Potential Energy from newtons law of gravity that is

[tex] U_{g} = \frac{\-GMM}{r} [/tex]

I set the 0 of potential energy at the point when the planet's center's crash together. So the change in potential will be the starting point minus the point when the planets just hit (when the distance between them is twice the radius of Jupiter- their outer edges are just touching). Mathmatically this is:

[tex] \Delta U_{g} = \frac{\-GMM}{1.0014 X 10^11 m} - \frac{\-GMM}{1.398 X 10^8} [/tex]

Now I should be able to just set the change in kinetic energy equal to the change in potential, but I'm not gettign the right answer. Can someone show me whats wrong with my reasoning. For anyone who has the book this problem is in Knight Chapter 12 #49. Thanks Alot.

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# Homework Help: Newton's Law of Gravity and Potential Energy

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