Originally Posted by
Norske
No, I'm just giving an easy way to get to Momentum, the basis for the Taylor and the Ed Matunas formulas. Whether KE or M is appropriate, think of elastic and inelastic impacts. A simple example of an elastic collision is those desk toys consisting of 5 steel balls hanging from a beam. Pull one back, let go and only one is displaced from the other end. Pull two back and let go, two are displaced. There is no deformation of any of the steel balls. Another example is in pool, billiards, snooker,etc.
A collision between two cars is inelastic. Lots of deformed sheet metal, lots of heat generated. Obviously, a bullet hitting an animal isn't elastic. There is deformation of both flesh and bullet and broken bone.