 After 100% inelastic collision, the second extreme craze is 100% elastic collision. What's happening in 100% elastic collision is that two objects that initially travel in different directions collide and then continue to travel in different directions after the collision. A classical example will be pool billiard when two balls collide. Now, in 100% elastic collision, kinetic energy is conserved. So you have kinetic energy final is equal to kinetic energy initial, meaning 1 half m 1 v final 1 squared plus 1 half m 2 v final 2 squared is equal to 1 half m 1 v initial 1 squared plus 1 half m 2 v initial 2 squared. If there is not 100% of kinetic energy that is conserved, but the part is used up by deformation energy, then that's what we have like a realistic collision, something between 0 and 100%. Now, the energy one is a bit complicated, but the linear momentum equation is exactly the same as for the inelastic collision, which is it is conserved. So we have a final momentum is equal to the initial momentum. So we have m 1 v 1 final vector plus m 2 v 2 final vector is equal to m 1 v 1 initial vector plus m 2 v 2 initial vector. So in 100% elastic collision, we can have one equation from conservation of energy, and then we can have for each dimension in which we're traveling one equation from conservation of linear momentum.