A moving H-atom makes a head on perfectly inelastic collision with a stationary `Li^(++)` ion. Just before collision, both `- H` and `Li^(++)` are in their first excited state. Immediately after collision H was found to be in ground state and `Li^(++)` was in its second excited state. Find the kinetic energy of H – atom before collision. No photon is emitted in the process. Assume that mass of `Li^(++)` is nearly 7 times the mass of H.

Answer

`7.77 keV`