Two circular discs of radius each 10 cm are joined at their centres… | JEE Main 2026 (28 Jan, Shift 1)

Q32JEE Main 2026 · 28 JAN · SHIFT 1Medium

Moment of Inertia & Radius of Gyration

Two circular discs of radius each 10 cm are joined at their centres by a rod of length 30 cm and mass 600 gm as shown in figure.

If the mass of each disc is 600 gm and applied torque between two discs is $43 \times 10^{5}$ dyne.cm, the angular acceleration of the discs about the given axis $AB$ is $\underline{\qquad}\ \text{rad/s}^2$ .

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Answer: (d)

In CGS: discs $600\text{ g}$ , $r = 10\text{ cm}$ , centres at $10\text{ cm}$ and $20\text{ cm}$ from AB; AB lies along a diameter direction of each disc.
Discs: $\frac{mr^2}{4} + md^2$ : $15000 + 60000 = 75000$ and $15000 + 240000 = 255000\text{ g cm}^2$
Rod (30 cm, centre 5 cm from AB): $\frac{600 \times 900}{12} + 600 \times 25 = 60000\text{ g cm}^2$
$I = 3.9 \times 10^5\text{ g cm}^2$ , $\alpha = \frac{\tau}{I} = \frac{43 \times 10^5}{3.9 \times 10^5} \approx 11\text{ rad/s}^2$
So the answer is (d) 11.

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Moment of Inertia & Radius of Gyration question from JEE Main 2026 (28 Jan, Shift 1)

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