UPSEE 2018 Solved Paper

A disk of radius R and mass‌M is at equilibrium at position D on the smooth inclined plane which makes an angle θ with the vertical as shown. The disk's centre is attracted to a point A located at a vertical distance d above the surface as shown. Assume that the force of attraction is proportional to the distance from the disk's centre of mass to point A, i.e. assume that F=−kr, where r is the distance from the point A to the disk's centre of mass and k is constant. Then, distance BD is