When a stationary nucleus decays, it emits an electron with kinetic energy
E = 1.73 MeV and a neutrino with energy E = 1 MeV perpendicular to
e v
the direction of electron motion. The rest mass of neutrinos is zero. What
is the kinetic energy of the nucleus if the remaining mass of the nucleus is
M = 3.9⋅10−22 g?