21. Kinetic Theory of Ideal Gases

1.0 mol of argon has 3100 J of thermal energy. What is the gas temperature in °C?

A rubidium atom (m = 85 u) 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 ⋋ = 780 nm. Determine the resulting (nonrelativistic) recoil speed v of the atom.