1. The problem statement, all variables and given/known data What is the velocity of an electron in the hydrogen atom if the centripetal force is supplied by the Coulomb's force between the electron and proton? 2. Relevant equations The radius of the electron orbit is 5.29 X 10^-11 3. The attempt at a solution The answer in the back of the book is 2.19 X 10^6 m/s. I am not really sure how to start this problem since it only gives me the radius. Please help!