1. The problem statement, all variables and given/known data http://www.math.udel.edu/~moulton/Apollo%20EC.pdf [Broken] This is the full problem that I am working on for my ODE class. 2. Relevant equations I would figure acceleration equals the second derivative so a=d^2s/dt^2 and V=ds/dt like the hint says. 3. The attempt at a solution I looked over the examples of Nonlinear ODEs but they all have 2 variables instead of just one like this one. I was looking for an integrating factor but none of that works out I think. I tried to integrate it by parts twice but that lead to a jumbled mess. I tried to subsitute s in terms of V but that didnt work to well either. For me the only trouble that I am having is the fact that its a nonlinear problem with really only one variable because V is in terms of S And looking at a,b and c all of them dont deal with the s variable. I'm not too sure where in the math that it gets canceled out. In fact each step seems to reduce the variables needed. Im just not sure how to tackle the problem. The math shouldnt be bad but I cant find a place to start.