Electric Potential Difference...Please HELP!!! 1. The problem statement, all variables and given/known data What potential difference is needed to accelerate a He+ ion (charge +e, mass 4u) from rest to a speed of 2690000 m/s? 2. Relevant equations 3. The attempt at a solution Change in V = Change in K Change in V = 1/2 mv^2 But what dose mass = 4u mean? What is u???