as alluded to in the title, this isn't so much a "problem" as a concept for a lab/experiment we performed. so, for some reason I was sure that a collision between two hockey pucks of roughly equal masses would result in an elastic collision, but I calculated the KE, and the two values were different, meaning it wasn't elastic. is this, uh, okay? from the way our professor explained the concept of elastic collisions[though not necessarily the lab itself], this type of collision[two similar masses moving at angles and producing a glancing collision] should result in conserved KE. but, maybe I just didn't understand what he was trying to say.