Four charges are fixed at the corners of a square centered at the origin as follows: q at (−a, +a); 2 q at (+a, +a); −3 q at (+a, −a); and 6 q at (−a, −a). a fifth charge +q with mass m is placed at the origin and released from rest. find the speed when it is a great distance from the origin, where the potential energy of the fifth charge due to the four point charges is negligible.