Here's a classical mechanics problem I'm having some trouble with: A particle of mass m moves on the positive x axis under the influence of a force F=-K/x^2, where K is a positive constant. The particle is released from rest at x=R at time 0. Find the velocity as a function of x as it accelerates towards the origin. Find the time at which it reaches the origin (you may need integral tables). The problem that I'm having is that the function that I get isn't defined at either x=R, or at x=0. Any help would be appreciated!