A light photon of wavelength `lambda_(0)` is absorbed by an atom of mass m at rest in ground state. The atom is free to move. The atom after absorbing the incident photon, emits another photon in direction opposite to that of the incident photon and returns back to its ground state. In the process the atom acquires a kinetic energy k. Find `lambda_(0)` in terms of k and m.

Answer

`lambda_(0) = (2h)/(sqrt(2mk) + (k)/(c))`