A circular disc $D _ { 1 }$ of mass $M$ and radius $R$ has two identical discs $D _ { 2 }$ and $D _ { 3 }$ of the same mass $M$ and radius R attached rigidly at its opposite ends (see figure). The moment of inertia of the system about the axis $\mathrm { OO } ^ { \prime }$, passing through the centre of $D _ { 1 }$, as shown in the figure, will be (1) $\mathrm { MR } ^ { 2 }$ (2) $3 \mathrm { MR } ^ { 2 }$ (3) $\frac { 4 } { 5 } \mathrm { MR } ^ { 2 }$ (4) $\frac { 2 } { 3 } \mathrm { MR } ^ { 2 }$
A circular disc $D _ { 1 }$ of mass $M$ and radius $R$ has two identical discs $D _ { 2 }$ and $D _ { 3 }$ of the same mass $M$ and radius R attached rigidly at its opposite ends (see figure). The moment of inertia of the system about the axis $\mathrm { OO } ^ { \prime }$, passing through the centre of $D _ { 1 }$, as shown in the figure, will be\\
(1) $\mathrm { MR } ^ { 2 }$\\
(2) $3 \mathrm { MR } ^ { 2 }$\\
(3) $\frac { 4 } { 5 } \mathrm { MR } ^ { 2 }$\\
(4) $\frac { 2 } { 3 } \mathrm { MR } ^ { 2 }$