A neutron moving at a speed v undergoes a head-on elastic collision with a nucleus of mass number A at rest. The ratio of the kinetic energies of the neutron after and before collision is :

Options

A. `((A-1)/(A+1))^(2)`
B. `((A+1)/(A-1))^(2)`
C. `((A)/(A+1))^(2)`
D. `((A)/(A-1))^(2)`