6. (a) a small styrofoam bead with a mass of 18.2 g and a charge of −0.682 μc is suspended in equilibrium above the center of a large, horizontal sheet of plastic that has a uniform charge density on its surface. find the charge per unit area on the plastic sheet (in μc/m2). (b) what if? what are the magnitude and direction of the acceleration of the piece of styrofoam if its charge is doubled? (enter the magnitude in m/s2.)