A point charge Q is fixed at the center of an insulated disc of mass M & radius R.The disc is resting on a rough horizontal plane.Another charge (-Q) is fixed vertically above the center of the disc along a height h.If the disc is displaced slightly in the horizontal direction & released.Find the period of oscillation of the disc. Note -Don't give me only hint as i already got the hint as i tried but can't solve it .So,give me the solution with the explanation and also with the diagram.