1. The problem statement, all variables and given/known data Central force F=-ar/(r^3) & Central potential energy,U=-(a/r) (not U_eff) Find the nature of orbits if (i)a>0 and (ii)a<0 2. Relevant equations 3. The attempt at a solution If we remember the attractive central force E=E(r) diagram,i.e.the one showing the graph of U_eff,we only need to know E_total=K+U. Where only PE is given. We see, U= -integration[F.dr]=integration[dW]=-integration[dK]=-K Then K=a/r and U=-(a/r) So,the E=K+U=0 Then in positive and negative both caes we get a parabolic orbit. Please check if i am correct.