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Answer in brief: A uniform disc and a hollow right circular cone have the same formula for their M.I. when rotating about their central axes. Why is it so?

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Question

Answer in brief:

A uniform disc and a hollow right circular cone have the same formula for their M.I. when rotating about their central axes. Why is it so?

Short/Brief Note
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Solution

A uniform disc and a hollow right circular cone have the same formula for their moment of inertia.

`"MI" = 1/2mr^2`

This is due to the fact that when a hollow right circular cone is sliced along its slanting side and the metal is stretched out, the cone's surface becomes a circle. This shape is similar to that of a disc, which is a circular as well. As a result, they both share the same moment of inertia formula.

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Chapter 1: Rotational Dynamics - Exercises [Page 24]

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Balbharati Physics [English] Standard 12 Maharashtra State Board
Chapter 1 Rotational Dynamics
Exercises | Q 2.5 | Page 24

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