Imagine that you replace the block in the video with a happy or sad ball identical to the one used as a pendulum, so that the sad ball strikes a sad ball and the happy ball strikes a happy ball. the target balls are free to move, and all the balls have the same mass. in the collision between the sad balls, how much of the balls' kinetic energy is dissipated?

a) none of it
b) all of it
c) half of it
they refer to a "sad ball" as a ball which doesn't bounce at all. example, if you dropped the ball on the ground it would simply stop (like clay) --> so it's a completely inellastic collision.

the answer is half of it, but could someone explain how we arrive to this conclusion? like maybe using some formulas?