One way that scientists measure the mass of an unknown particle is to bounce a known particle, such as a proton or an electron, off the unknown particle in a bubble chamber. the initial and rebound velocities of the known particle are measured from photographs of the bubbles it creates as it moves; the information is used to determine the mass of the unknown particle. (a) if a known particle of mass m and initial speed v0 collides elastically, head-on with a stationary unknown particle and then rebounds with speed v, find an expression for the mass of the unknown particle in terms of m, v, and v0. (b) if the known particle is a proton and the unknown particle is a neutron, what will be the recoil speed of the proton and the final speed of the neutron?