In part (a) of the gure an electron is shot directly away from a uniformly charged plastic sheet, at speed v5 = 1.50 x 105 m/s. The sheet is nonconducting, at, and very large. Part (b) of the gure gives the electron's vertical velocity component v versus time tuntil the return to the launch point. What is the sheet's surface charge density? Assume t5 = 24.0 ps. (a) Number i ! Units C/m"2 v