1. The problem statement, all variables and given/known data 2. Relevant equations on image 3. The attempt at a solution The first thing I did was use the second equation to get Theta dot = L/mr2 Which I then subbed into the first equation to eliminate Theta dot. Now I need everything in terms of r, and this is where I get stuck. If I just find the second derivative of r (r double dot), then sub it back in, Im left with all kinds of Thetas, but I need f as a function of r. How do I proceed here? Any help is greatly appreciated!! Thanks!