The rest energy of an electron is 0.511 MeV,and its rest mass is 0.511 MeV/c². If an electron has a speed of 99% that of light,what fraction of its total energy is in the form of kinetic energy? A)76% B)50% C)68% D)86%

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Quizplus · Accepted Answer

The total energy of the electron is given by E = γmc², where γ is the Lorentz factor. At 99% the speed of light, γ ≈ 7.09. The rest energy is 0.511 MeV, so the total energy is 7.09 * 0.511 MeV ≈ 3.62 MeV. The kinetic energy is the total energy minus the rest energy, which is 3.62 MeV - 0.511 MeV = 3.109 MeV. The fraction of the total energy that is kinetic is 3.109 MeV / 3.62 MeV ≈ 0.86, or 86%.

The Rest Energy of an Electron Is 0