(a) A rubidium atom (m = 85u) is at rest with one electron in an excited energy level. When the electron jumps to the ground state, the atom emits a photon of wavelength λ = 780 nm. Determine the resulting (nonrelativistic) recoil speed v of the atom.
(b) The recoil speed sets the lower limit on the temperature to which an ideal gas of rubidium atoms can be cooled in a laser-based atom trap. Using the kinetic theory of gases (Chapter 13), estimate this "lowest achievable" temperature.