' P ' and ' Q ' are fixed points in same plane and mass ' m ' is tied by string as shown in figure. If the mass is displaced slightly out of this plane and released, it will oscillate with time period (\mathrm{PQ}=2 \mathrm{~d}, \mathrm{PR}=\mathrm{QR}=\mathrm{L})(\mathrm{g}= gravitational acceleration)