Electric Potential-- quick question about process 1. The problem statement, all variables and given/known data An alpha particle with kinetic energy 10 MeV makes a head-on collision with a lead nucleus at rest. What is the distance of closest approach of the two particles? (Assume that the lead nucleus remains stationary and that it may be treated as a point charge. The atomic number of lead is 82. The alpha particle is a helium nucleus, with atomic number 2.) 2. Relevant equations V=kq/r 3. The attempt at a solution http://www.solvephysics.com/electricity_problem26.shtml I tried going by this site to solve this. I would just like to know why in the Einitial equation they multiply the 10MeV by 1.6e-19. Why do they do that? I don't understand. Thanks!