Two 2.40cm--diameter disks spaced 1.90mm apart form a parallel-plate capacitor. The electric field between the disks is 5.20×10^5 V/m. a)What is the voltage across the capacitor? b)An electron is launched from the negative plate. It strikes the positive plate at a speed of 2.40×10^7m/s . What was the electron's speed as it left the negative plate?