Two 2.5-cm-diameter-disks spaced 1.5 mm apart form a parallel-plate capacitor. The electric field between the disks is 4.2×105 V/m. A) What is the voltage across the capacitor? B) How much charge is on each disk? C) A positron (same mass as electron, and same charge, except positive) is launched from the positive plate. It strikes the negative plate at a speed of 2.2×107 m/s . What was the positron's speed as it left the positive plate?