1. The problem statement, all variables and given/known data What is the kinetic energy given to the proton in the decay of a neutron when: a) The electron has negligibly small kinetic energy b) The neutrino has negligibly small kinetic energy 2. Relevant equations Q = (mn - mp - me - mv ) c2 = .782MeV Where T is kinetic energy, and the neutron is at rest: Q = Tp + Te + Tv 3. The attempt at a solution Now my thoughts are similar for both part a) and b): For a, if the electron has zero kinetic energy, then by conservation of momentum, the proton and the neutrino must have equal and opposite momentums. But from lecture, my professor explicitly wrote: Since mp >> me, and mp >> mv, Tp << Te, and Tp << Tv, so the Q value is practically shared between the electron and the neutrino. and when Tv = 0, Te = Q So is this a trick question then? Is the kinetic energy given to the proton always going to be essentially zero in part a) and b) , since it is so massive?