A point charge of +Q is placed at the center of a square, and a second point charge of -Q is placed at the upper-left corner. It is observed that an electrostatic force of 4.0 N acts on the positive charge at the center. What is the magnitude of the force that acts on the center charge if another charge of -Q is placed at the lower-left corner? E, E2 E3 E4 Ans: zero 2.8 N +Q 4.0 N Q 5.6 N 8.0 N 2F=? 74=F 4x cos(45) = 2.82 2.82+28255.6