Randall D. Knight — Impulse and Momentum: Problem 69

A neutron is an electrically neutral subatomic particle with a mass just slightly greater than that of a proton. A free neutron is radioactive and decays after a few minutes into other subatomic particles. In one experiment, a neutron at rest was observed to decay into a proton (mass \(1.67 \times 10^{-27} \text{ kg}\)) and an electron (mass \(9.11 \times 10^{-31} \text{ kg}\)). The proton and electron were shot out back-to-back. The proton speed was measured to be \(1.0 \times 10^5 \text{ m/s}\) and the electron speed was \(3.0 \times 10^7 \text{ m/s}\). No other decay products were detected. a. Did momentum seem to be conserved in the decay of this neutron? b. If a neutrino was emitted in the above neutron decay, in which direction did it travel? Explain your reasoning. c. How much momentum did this neutrino “carry away” with it?