Here is a little problem i am having with elastic colisions. With inelastic colisions, momentum is conserved but kinetic energy is not. And so from my point of view it would be impossible to have an elastic colision where both momentum and kinetic energy would be conserved as if kinetic energy was conserved, momentum would rise. One solution i thought up was that conserved did not mean "the same" That the momentum could rise. I also have been thinking that the two balls will move off with the same speed as each other. The question i am tackling involves two identical billard balls. Both of mass .2 kg One is stationary, and the other is traveling at 2.5 ms towards the stationary From E = .5mv^2 i found the initial kinetic energy to be .625 j and so this amount of kinetic energy must be present in the final velocity of the balls once they colide. I am asked to find the final velocity of the two billard balls but am stuck.