I am reading a book about general physics kinematics, optics, waves, etc. It focuses more on history than on explaining equations or sample problems. One of the sample problems in Electric Fields section asks to find energy and speed when a positron moves from one plate that has electric potential of 1e6 V to another that has zero electric potential. As far as the energy is concerned it is the potential which equals U=1e6 x 1.6e-19 = 1.6e-13 which is what the answer is at the back of the book states. But for the speed I get a different answer. I assume that potential is turned in to kinetic as positron reached the other plate so: Ek=0.5mvv then v=sqr(2Ek/m) m=9.1e-31 Kg Ek=1.6e-13 so from above v=5.9e8 but in the book the answer is 1.4e7m/s What am I missing or not understanding?