Mass of the disc = 9M Mass of removed portion of disc = M The moment of inertia of the complete disc about an axis passing through its centre O and perpendicular to its plane is I1=
9
2
MR2 Now, the moment of inertia of the disc with removed portion I2=
1
2
M(
R
3
)2=
1
18
MR2 Therefore, moment of inertia of the remaining portion of disc about O is I=I1−I2 =