A uniformly charged ring has a radius 80.0 cm and a charge 19.5 μC. A small object with mass 11.0 g and charge -0.500 μC is at the center of the ring, but it is free to move along the axis of the ring. (It is not free to move off the axis.) Suppose the small object is displaced along the axis a distance z from the center of the ring. It is only displaced a very small amount, so z is much smaller than the radius of the ring. Show that the force is roughly proportional to the displacement, that is, that F≈αz, and find a numerical value for α.