Two disks are mounted on low-friction bearings on a common shaft. The first disc has rotational inertia I and is spinning with angular velocity ω . The second disc has rotational inertia 2I and is spi

Question

Two disks are mounted on low-friction bearings on a common shaft. The first disc has rotational inertia I and is spinning with angular velocity $ω$ . The second disc has rotational inertia 2I and is spinning in the same direction as the first disc with angular velocity $2 ω$ , as shown. The two disks are slowly forced toward each other along the shaft until they couple. Their final common angular velocity is :

Options:

Answer:

A

Solution:

No external torque, so angular momentum is conserved.

$L_{i} = I ω + 2 I (2 ω) = 5 I ω$

$I_{total} = I + 2 I = 3 I$

$ω_{f} = \frac{5 I ω}{3 I} = \frac{5 ω}{3}$

Answer A.

TestHub · Accepted Answer

No external torque, so angular momentum is conserved. L i ​ = I ω + 2 I ( 2 ω ) = 5 I ω I total ​ = I + 2 I = 3 I ω f ​ = 3 I 5 I ω ​ = 3 5 ω ​ Answer A.

Physics - Rotation Question with Solution | TestHub

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JEE Main 2027 (Class 12+)