Suppose that an atomic nucleus of mass m2 collides with a second nuclear particle of mass m1. If the atomic nucleus is initially at rest, and the velocity of the second nuclear particle is reduced by...

Suppose that an atomic nucleus of mass m2 collides with a second nuclear particle of mass m1. If the atomic nucleus is initially at rest, and the velocity of the second nuclear particle is reduced by 50%, what is the mass of the atomic nucleus? Assume that the mass of the second nuclear particle is 1 AMU.