1. The problem statement, all variables and given/known data A particle of mass m and kinetic energy K strikes and combines with a stationary particle of mass 2m, producing a single composite particle of mass √17 m. Find the value of K 2. Relevant equations E= γmc^2 , p = λmv 3. The attempt at a solution I have tried many times at this and have used the conservation of energy and conservation of momentum but I seem to get nowhere. The equations are definitely solvable and this seems to just be algebraic manipulation. My question is whether there is any way to simplify these problems as I just cannot get an expression for K without the other variables, this problem keeps cropping up in other questions too!