1. The problem statement, all variables and given/known data A photon and alpha particle are accelerated from rest through the same potential difference. After acceleration what is the ratio kinetic energy of alpha particle / kinetic energy of proton? 2. Relevant equations I guess I have to use eV = 1/2mv^2 3. The attempt at a solution I dont know what value have to be used in place of e in equation eV = 1/2mv^2 the mass of alpha particle is approximately 4 times of photon and that's all i know I guessed the answer as 4 but the answer was 2 I think there is something to do with the velocity of alpha particle and photon but i'm stucked can not think of anything..