A semicircular lamina has radius R and diameter D. Determine the moment of inertia about the diametrical axis as shown below?

F7 Savita ENG 21-12-23 D2

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SSC JE Civil 10 Oct 2023 Shift 1 Official Paper-I
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  1. \( \frac{\pi R^4}{8} \)
  2. \( \frac{\pi D^4}{32} \)
  3. \( \frac{\pi R^4}{16} \)
  4. \( \frac{\pi D^4}{64}\)

Answer (Detailed Solution Below)

Option 1 : \( \frac{\pi R^4}{8} \)
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Detailed Solution

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Explanation:

The moment of inertia of a circular lamina is

\(I = \frac{π }{{64}}{D^4}\) = π(2R)4/64 = πR4/4 

The moment of inertia about the diametrical axis semicircular lamina is

= I/2 = (πR4/4)/2 = πR4/8

Additional Information

The formula of the moment of inertia for various other figures is given below.

Moment of inertia of different section:

Shape of cross-section

INA

Ymax

Z

Rectangle

\(I = \frac{{b{d^3}}}{{12}}\)

\({Y_{max}} = \frac{d}{2}\)

\(Z = \frac{{b{d^2}}}{6}\)

Circular

\(I = \frac{π }{{64}}{D^4}\)

\({Y_{max}} = \frac{d}{2}\)

\(Z = \frac{π }{{32}}{D^3}\)

Triangular

\(I = \frac{{B{h^3}}}{{36}}\)

\({Y_{max}} = \frac{{2h}}{3}\)

\(Z = \frac{{B{h^2}}}{{24}}\)

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