I'm stuck on this question. I've been trying to use Newtonian methods to solve this question by using f =m v squared over r. But I don't know how to use the potential given in the problem with this approach. Please help.

Consider two particles of masses m, and m2 interacting with potential V(r). (a) Show that a circular orbit of radius ro is only stable when V"(ro) 0) have stable, circular orbits