PhysicsLAB AP Free Response Question
2007 B7

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It is possible for an electron and a positron to orbit around their stationary center of mass until they annihilate each other, creating two photons of equal energy moving in opposite directions. A positron is a particle that has the same mass as an electron and equal but opposite charge. The amount of kinetic energy of the electron-positron pair before annihilation is negligible compared to the energy of the photons created.
 (a) Calculate, in eV, the rest energy of a positron.

 (b) Determine, in eV, the energy each emitted photon must have.

 (c) Calculate the wavelength of each created photon.

 (d) Calculate the magnitude of the momentum of each photon.

 (e) Determine the total momentum of the two-photon system.

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