Near the surface of the Earth there is an electric field of about 150 V/m which points downward. Two identical balls with mass m = 0.480 kg are dropped from a height of 1.90 m, but one of the balls is positively charged with q1 = 850 \mu C, and the second is negatively charged with q2 = -850 \mu C.
Use conservation of energy to determine the difference in the speed of the two balls when they hit the ground. (Neglect air resistance.)