1. The problem statement, all variables and given/known data Determine the total energy of an electron traveling at 0.98 c A) 0.25 MeV B) 0.51 MeV C) 0.76 MeV D) 1.8 MeV E) 2.6 MeV 2. Relevant equations KE = 1/2 mv^2 E=mc^2 (rest energy) 3. The attempt at a solution I had found the velocity for an electron by 0.98 * 3.0 *10^8. I squared that number and multiplied by the mass of the electron (9.11 * 10^-31 kg) then multiplied by 0.5 This gave me 3.937 * 10^-14. I divided this by 1.6 * 10^-13 to get MeV which gave me an answer of 0.246 MeV. That would be answer A, but the correct answer was E. I also took into account for a possible Rest energy, which you would use E=mc^2. Adding up what I got for rest energy and my original answer which gave me A, resulted in the answer for C. I'm still not sure how the answer E came about.