A stage crew member uses a pulley system to close the curtains on stage. If he does 620 Joules of work and the pulley system does 415 Joules of work, the efficiency of the pulley system is

Four objects each with charge +2.0×10−7c are located at the corners of a square whose sides are 2.0 m long. part a what quantities can be determined using this information? check all that apply. the electric force on a charged object placed at the center of the square. the mass of each object. the total electric potential energy of the system consisting of the four charged objects. part b find the electric force on a charged object placed at the center of the square.