A disc of radius R=10 cm oscillates as a physical pendulum about an axis perpendicular to the plane of the disc at a distance r from its centre. If r=R4, the approximate period of oscillation (in second) is (Take g=10 m s-2)

Time period of a physical pendulum is T=2πImghwhere I is the moment of inertia of the pendulum about an axis through the pivot, m is the mass of the pendulum and h is the distance from the pivot to the centre of mass. In this case, a solid disc of R oscillates as a physical pendulum about an axis perpendicular to the plane of the disc at a distance r from its centre.∴I=mR22+mr2=mR22+mR42=mR22+mR216=9mR216  ∵r=R4  Here, R=10 cm=0.1 m,h=R4 ∴  T=2π9mR216mgR4=2π9R4g =2π9×0.14×10=2π×32×110=0.94 s