You have a lightweight spring whose unstretched length is 4.0 cm. first, you attach one end of the spring to the ceiling and hang a 3.0 g mass from it. this stretches the spring to a length of 5.4 cm . you then attach two small plastic beads to the opposite ends of the spring, lay the spring on a frictionless table, and give each plastic bead the same charge. this stretches the spring to a length of 4.7 cm . what is the magnitude of the charge (in nc) on each bead?