1. The problem statement, all variables and given/known data A particle moves under the action of a central force in a spiral orbit given by r=a*theta. Show that the force is f(r) = (-L^2/mr^3)*[1 + (a^2)/(r^2)] 2. Relevant equations 3. The attempt at a solution I know how to do the problem, but I keep ending up with a factor of 2 for the a^2 term. Any pointers on how to fix this? Thanks for the help!