1. The problem statement, all variables and given/known data 2. Relevant equations [PLAIN]http://upload.wikimedia.org/math/7/7/4/7745116605c54295c6c3b696cea2d39f.png[/CENTER][/URL] [Broken] 3. The attempt at a solution I have gotten these problems wrong too many times. I know that I have to apply both the conservations of momentum and kinetic energy, but for some reason I can't come up with the right answer. m1=21.3g v1=24.6cm/s m2=11.6g v2=11.3cm/s I don't know how to solve these relations with two unknowns. I've tried using substitution from the kinetic energy equation, but I still got it wrong for some reason. Any help for a desperate physics student?