1. The problem statement, all variables and given/known data A proton is traveling to the right at 2.0x10^7 m/s. It has a head on perfectly elastic collision with a carbon atom. The Mass of the Carbon atom is 12 times the mass of the proton. What are the speed and direction of each after collision? 2. Relevant equations Ke=1/2M*V^2 P(momentum)=M*V 3. The attempt at a solution p=proton c=carbon After the collision: 1/2MpVpf^2 + 1/2McVcf^2=1/2MpVp^2 MpVpf+McVcf=MpVp Solved for: Vcf=Vp-Vpf/12 Vpf=Vp-12Vcf Vcf^2=Vp^2-Vpf^2/12 Vpf^2=Vp^2-12Vcf I've tried a few times but can figure out how to solve the rest of the equation. Every time I make a substitution I get MpVp=MpVp. Which I already knew, so I guess my algebra is a bit crap.(spelling too!) What is the next step? Thanks to anyone that helps.