[填空题]
In a photocell, ultraom cj8 )ej*;jeviolet*)m 3lw1a r8cthh8zsm (UV) light provides enough energy to some electrons in barium metal to eject them from a surface at high speed. See Fig. 17–33. To measure the maximum energy of the electrons, another plate above the barium surface is kept at a negative enough potenthtm 31a)ms zrclh 8*8wial that the emitted electrons are slowed down and stopped, and return to the barium surface. If the plate voltage is $-3.02V$ (compared to the barium) when the fastest electrons are stopped, what was the speed of these electrons when they were emitted? $ \times10^{6 }\,m/s$
