An electron initially 3.00 m from a non conducting infinite sheet of uniformly distributed charge is fired toward the sheet. the electron has an initial speed of 410m/s and travels along a line perpendicular to the sheet. when the electron has traveled 2.00 m , its velocity is instantaneously zero, and it then reverses its direction. a- what is the surface charge density on the sheet? b- given the same initial velocity, from what distance should the electron be fired if it is to just reach the sheet?