Two identical point charges (q = +7.80×10−6 C) are fixed at opposite corners of a square whose sides have a length of 0.680 m. A test charge (q0 = −8.40×10−8 C), with a mass of 7.40×10−8 kg, is released from rest at one of the corners of the square. Determine the speed of the test charge when it reaches the center of the square.