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Question

For a symmetrical channel section with a moment of inertia I = 9.45 x $10^7$ $mm^4$ and an xx area A = 4500 $mm^2$, what is its radius of gyration $k_{xx}$ ? 

This question was previously asked in
RRB JE 2025 CBT 2 Mechanical and Allied Engg Question Paper English (2-Jul-2026) (Shift-1)
The correct answer is

144.92 mm

To find the radius of gyration k of the channel section, we can use the formula for the radius of gyration:

k = \sqrt{\frac{I}{A}}

Where:

  • I = Moment of inertia = 9.45 \times 10^7 \, \text{mm}^4
  • A = Area = 4500 \, \text{mm}^2

Substitute the values into the formula:

k = \sqrt{\frac{9.45 \times 10^7}{4500}}

Calculate the division inside the square root:

k = \sqrt{21000}

Now compute the square root:

k \approx 144.91 \, \text{mm}

Hence, the radius of gyration is approximately 144.92 mm.

This matches the correct answer, which confirms that the answer is 144.92 mm.

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