A football of radius R is kept on a hole of radius r (𝑟 < 𝑅) made on a plank kept horizontally. One end of the plank is now lifted so that it gets tilted making an angle 𝜃 from the horizontal as shown in the figure below. The maximum value of 𝜃 so that the football does not start rolling down the plank satisfies (figure is schematic and not drawn to scale) -