Question

Three charges are placed on the y axis. One charge of -3.2 micro-Coulombs is placed at y = 0, another charge of +2.6 micro-Coulombs is placed at y = -0.29 meters, and another unknown charge is placed at y = +0.51 meters. The total force on the charge at y = 0 due to the other charges is 3.8 Newtons in the positive y direction. What is the unknown charge at y = +0.51 meters in micro-Coulombs? If negative, include negative sign, but do not include positive sign if it is positive.