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#rotating disk

2 public questions tagged with this topic.

Moment of Inertia and Radius of Gyration

What is the effect of doubling the radius of a rotating disk on its moment of inertia, assuming mass remains constant?

For a disk, I = 12MR2. Doubling R increases R2 by a factor of 4, so I increases by a factor of 4 if M is constant. As per NCERT, applying relevant law/formula with correct units and sign convention leads to It quadruples. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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Vector Product and Rotational Kinematics

A uniform disk of mass 4kg and radius 0.5m rotates at 8rad/s. What is its angular momentum about its axis?

L = Iω. For a disk: I = 12MR2 = 12×4×(0.5)2 = 0.5kg m2. L = 0.5×8 = 4kg m2/s. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 4 kg m²/s. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

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