Approaches to Solving Galactic Dynamics Problems

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Homework Statement


http://www.mso.anu.edu.au/~kcf/ATA/ATA_assignment.pdf
Question One
Question 3b
Question 4b2. Homework Equations /Attempt at a solution
For the first one I am not even sure how to approach this, i understand/have poissons equation, general laws of motion and an idea of what relaxation time should be but I am not sure how to mathematically define it.

For 3b i get http://members.iinet.net.au/~housewrk/3rd/3b.jpg with L const and I am not sure how to go about solving that for the trajectory r(t)

For 4b I had to hunt around for Jeans' equation (not given in lectures, sort of a read outside the course thing) and using the info in the question used the reduced form of http://members.iinet.net.au/~housewrk/3rd/4b.jpg and again not sure how to get a density distribution out of that, as this form seems to treat it on a single particle basis. To be perfectly honest i thought it was a trick question as if theyre massless why should they be influenced by the potential? (we're only considering classical Newtonian mechanics in this course, not GR stuff)Any help (pointing out my stupid mistakes included, if youre nice) would be greatly appriciated =D

Thanks
-G
 
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