Question:

If the moment of inertia of a disc about an axis tangential and parallel to its surface be $I$, then what will be the moment of inertia about the axis tangential but perpendicular to the surface?

Updated On: Jun 20, 2022
  • $\frac {6}{5}I$
  • $\frac {3}{4}I$
  • $\frac {3}{2}I$
  • $\frac {5}{4}I$
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The Correct Option is A

Solution and Explanation

MI of disc about tangent in a place
$\hspace5mm = \frac {5}{4}MR^2=I \, MR^2= \frac {4}{5}I$
MI of disc about tangent perpendicular to plane
$\hspace10mm I'= \frac {3}{2}MR^2$
$\hspace10mm I'=\frac {3}{2}\bigg (\frac {4}{5}I\bigg )= \frac {6}{5}I$
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Concepts Used:

System of Particles and Rotational Motion

  1. The system of particles refers to the extended body which is considered a rigid body most of the time for simple or easy understanding. A rigid body is a body with a perfectly definite and unchangeable shape.
  2. The distance between the pair of particles in such a body does not replace or alter. Rotational motion can be described as the motion of a rigid body originates in such a manner that all of its particles move in a circle about an axis with a common angular velocity.
  3. The few common examples of rotational motion are the motion of the blade of a windmill and periodic motion.