A hydrogen atom in its ground state absorbs a 97-nm ultraviolet photon. It then emits one or more photons to return to the ground state.
(a) If the atom is at rest before absorbing the UV photon, what is its recoil speed after absorption?
(b) There are several different possible ways for the atom to return to the ground state. How many?
(c) For each of the possibilities in (b), give the wavelength of each photon emitted, and classify it as visible, UV, IR, x-ray, etc.