Question:
A neutron having kinetic energy $12.5 \mathrm{eV}$ collides with a hydrogen atom at rest. Neglect the difference in mass between the neutron and the hydrogen atom and assumes that the neutron does not leave its line of motion. Find the possible kinetic energies of the neutron after the event.
Solution:
In elastic collision between two bodies of equal masses, the velocity gets interchange. Since the hydrogen atom is at rest, after collision, the velocity of the neutron will be zero.