1. I have to use energy conservation to determine the forces acting on the particles. 2. An isolated system consists of two particles of masses m1 and m2, whose position vectors in an inertial frame are x1 and x2 and velocity vectors are v1 and v2. The interaction of the particles can be described by the energy function : E= 1/2m1(v1)^2 + 1/2m2(v2)^2 - (k/r^2) k is a positive constant r = mod(x1-x2) and is the magnitude of the seperation vector. 3. Do I have to differentiate E to get 1/2m1(a1)^2 + 1/2m2(a2)^2 - (k/r^2) and equate it to zero?