A neutron hits an atomic nucleus in a head-on collision and comes to a complete stop. It loses all of its kinetic energy in the process. If an identical neutron then scatters off of the same atomic...

A neutron hits an atomic nucleus in a head-on collision and comes to a complete stop. It loses all of its kinetic energy in the process. If an identical neutron then scatters off of the same atomic nucleus at an angle of 60° in the COM system, what fraction of its kinetic energy does it lose in a single elastic collision?