Example, cont.
We can use the Conservation of Energy including the formulas for kinetic energy and potential energy:
KEi + PEi = KEf + PEf + Elost , where
KE = (1/2)mv2 and PE = qV:
(1/2)mpvi2 + qpVi = (1/2)mpvf2 + qpVf + Elost
Since vi=0 and Elost=0, and bringing qpVf to the left side, we have: qp(Vi-Vf) = (1/2)mpvf2 .