1. The problem statement, all variables and given/known data For the decay " Uranium-232 ---> Thorium-228 + alpha particle ", What is the alpha particle's kinetic energy in the U-232 atom's rest frame? We are given the masses for each one. 2. Relevant equations E = mc^2 3. The attempt at a solution I tried mass(U-232) - (mass(Th-228) + mass(α) ) = 5.9 x 10^ -3 u And multiplied this by 931.5 to get E = 5.5 MeV. Is this all there is to it? I was unsure what it meant by "in rest frame of U-232"