Class 11 NEET Physics System of Particles and Rotational Motion

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
=

9MR2

2

−

MR2

18

=

40MR2

9