(1) Four positive charges +q sit in a plane at the corners of a square whose sides have length d as shown in figure below. A negative charge -q is placed in the middle of the square. (a) Neglecting gravity, draw a free-body diagram of electrostatic forces on the negative charge. (b) Calculate the magnitude of the net electric force on the 'negative charge.(c) Explain if the equilibrium point at the center is a stable equilibrium for the motion of the negative charge in the plane of the square? (5-points) + q +q -q d +