Aparticle of rest mass m, travelling at speed v in the x-direction, decays into two photons, moving in the positive and negative x-direction relative to the original par ticle. what are their energies? what are the photon energies and directions if the photons are emitted in the positive and negative y-direction relative to the original particle (i. e., perpendicular to the direction of motion, in the particle's rest frame)

Materials will have different energies associated with the electrons inside them. this is related to how strongly bound they are by their work function. if we sandwich a material with a very low energy between two materials with a high energy, we create a trap for an electron. if this trap is very narrow in one direction in comparison to the others, this is approximately a 1-dimensional box that confines the electron. what is the lowest energy of an electron in the box if the thinnest direction across the materials is 4.81 nm?