A solid disc of radius 0.30 m is suspended from a wire. The time period of its  angular oscillation is 3.14 s, if the torque constant of the wire is  1.2×10−3  Nm/rad.  Then the mass of the disc is

For torsional pendulam,  T=2πIcHence moment of inertia will be   I=T24π2cI=π24π2×1.2×10−3  I=1.2×10−34=0.3×10−3    kg  m2For a disc moment of inertia is MR22Hence  MR22=0.3×10−3  M=0.6×10−30.3×0.3  M=6.67  ×10−3   kg M=6.67 gram