Four identical particles with charge -3 C are located at the corners of a square. The square's sides are 3 cm in length. A fifth

Four identical particles with charge -3 μC are located at the corners of a square. The square's sides are 3 cm in length. A fifth particle of charge -12 μC is placed directly at the center of the square. A.) What is the magnitude of the total electric force on any one of the four particles at the corners? B.) If you could adjust the charge of the particle at the center, what should you choose so that the net electric force on any of the corner particles is zero?