1. The problem statement, all variables and given/known data In the reference frame S', two protons, each moving at .5c, approach each other head on. Calculate the total kinetic energy of the two protons in frame S', and calculate the total kinetic energy of the two protons as seen in reference frame S which is moving with one of the protons. 3. The attempt at a solution So for the first part apparently the answer i'm looking for is 290MeV v = .5c so γ = 1.1547 using 1/2 mv^2 m = 1.6726E-27 v = .5(3E8) and then multiplying this times two for two protons and 1.15 from gamma, then converting that to eV by 1J = 6.24E18 eV I get 270MeV.. back of the book says 290 MeV.. what am I doing wrong ;-(?