A neutron at rest decays into a proton plus an electron. The conservation of momentum implies that the electron and proton should have equal and opposite momentum. However, experimentally they do not. This apparent nonconservation of momentum led Wolfgang Pauli to suggest in 1931 that there was a third, unseen particle emitted in the decay. This particle is called a neutrino, and it was finally observed directly in 1957. Suppose that the electron has momentum p = 4.65 × 10⁻²² kg·m/s along the negative x direction and the proton (m = 1.67 × 10⁻²⁷ kg) moves with speed 2.93 × 10⁵ m/s at an angle 17.9° above the x axis. Find the momentum of the neutrino. (The kinetic energy of the electron is comparable to its rest energy, so its energy and momentum are related relativistically rather than classically. However, the rest energy of the proton is large compared with its kinetic energy so the classical relation E = ½mv² = p²/2m is valid)