The moment of inertia of a thin rod about an axis passing through its mid point and perpendicular to the rod is $2400\, g\, cm^2$ . The length of the $400\, g $ rod is nearly:
Answer & explanation
Correct answer: option 1
The correct answer is option (1) : 8.5 cm
Moment of inertia of road $=I=\frac{ml^2}{12}$
$⇒2400=400\frac{l^2}{12}$
$⇒72=l^2$
$⇒l=\sqrt{72}=8.48\, cm ≈8.5\, cm $