HallsofIvy

gammamcc, I think you are missing the point. The problem is not to integrate [itex]d^2r/dt^2= 1/r^2[/itex]. He's alread done that. That results in
[tex]v= \frac{dr}{dt}= \sqrt{c_1- \frac{2}{r}}[/tex]
The question is how to integrate that.