1. The problem statement, all variables and given/known data Is the kinetic energy of an electron the same in all frames of reference? 2. Relevant equations I think that the kinetic energy of an electron is E = hc / λ. However, I am not sure: I got this from searching Google rather than learning it myself. 3. The attempt at a solution I think that, due to length contraction, the wavelength is different in both frames, and hence it is not the same in all frames of reference. However, I am not sure about this.