Here is a problem dealing with the most general form of an elastic collision (two things collide
and bounce off of each other).
There is one car, call it car #1, moving toward the right. It has an initial speed v1i= m/s,
and a mass of m1= kg.
There is another car, call it car #2. It can be moving, or not. Enter 0 if you want
it at rest. Enter a + speed if you want it moving toward the right, or a - speed if you want it
moving toward the left. The speed of car #2 is v2i= m/s and the mass
of car #2 is m2= kg.
The problem here is to calculate what the speed of each car will be after the collision.