Question

A nucleus, initially at rest, decays radioactivly, leaving a residual nucleus. In the process, it emits two paricles horizontally: an electron with momentum 9.0 x 10^-21 kg m/s [E] and a neutrino with momentum 4.8 x 10^-21 kg m/s [S]. In what direction does the residual nucleus move? What is the magnitude of its momentum?

Answer 1

add the two momentum vectors, then the negative of it is the momentum of the nucleus.