I was going to put this up in the homework forum, but I feel the folks down here are more capable of helping me out. I have to do an assignment, but I cannot go in for office hours to get help from my professor. Regretfully, I lost the sheet and forgot to grab another until just a few days ago and now I'm on my own. All I really need are the formulas. Here goes: 1. I can do part a, but I am completely flabbergasted at part b. 2. Need formula 3. Need formula 4. I believe I can do this one, but don't I need the velocity of the coma cluster to solve it?