In a photocell, ultraviolet light provides sufficient energy to some electrons in barium metal to eject them from the surface at high speed. See Fig. 23-36. To gauge the maximum energy of the electrons, another plate above the barium surface is kept at a negative sufficient potential that the emitted electrons are slowed down and stopped, and return to the barium surface. If the plate voltage is -3.02V when the fastest electrons are stopped, what was the speed of these electrons when they were emitted?