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Moment of Inertia and Radius of Gyration

This category covers the calculation and application of moment of inertia and radius of gyration for rigid bodies. Learn how mass distribution affects rotational motion through solved problems and theory.

51 questions

A 6kg particle moves with velocity v\=3j^m/s at r\=−4i^m. What is the magnitude of its angular momentum about the origin

L = r×p = |i^j^k^−400030| = k^((−4)×3−0×0) = −12k^kg m2/s. Magnitude = 12kg m2/s. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 12 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.

A 4kg particle moves with velocity v\=3i^+5j^m/s at r\=−2i^m. What is the z-component of its angular momentum?

L = r×p = |i^j^k^−200350| = k^((−2)×5−0×3) = −10k^kg m2/s. Z-component = −10kg m2/s. As per NCERT, applying relevant law/formula with correct units and sign convention leads to -10 kg m²/s. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

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

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.

A uniform square lamina of side 4m and mass 8kg has one corner at the origin and lies along the x- and y-axes. What is t

For a uniform square, the center of mass is at the centroid. Vertices: (0,0),(4,0),(0,4),(4,4). CM: X = 0+42 = 2, Y = 0+42 = 2. Position: (2,2)m. As per NCERT, applying relevant law/formula with correct units and sign convention leads to (2,2). This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

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

A wheel with moment of inertia 8kg m2 rotates at 2rad/s. A torque of 16Nm acts for 3s. What is its final angular velocit

α = τI = 168 = 2rad/s2. Δω = αt = 2×3 = 6rad/s. ω = ω0+Δω = 2+6 = 8rad/s. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 8 rad/s. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

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

A solid sphere of mass 2kg and radius 0.6m rotates about its center at 5rad/s. What is its rotational kinetic energy?

I = 25MR2 = 25×2×(0.6)2 = 0.288kg m2. K = 12Iω2 = 12×0.288×(5)2 = 0.144×25 = 3.6J. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 3.6 J. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

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

A wheel with moment of inertia 5kg m2 rotates at 3rad/s. A torque of 10Nm acts for 5s. What is its final angular velocit

α = τI = 105 = 2rad/s2. Δω = αt = 2×5 = 10rad/s. ω = ω0+Δω = 3+10 = 13rad/s. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 13 rad/s. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

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

A force F\=7i^+3j^N acts at r\=−2i^+1j^m. What is the magnitude of the torque about the origin?

τ = r×F = |i^j^k^−210730| = k^((−2)×3−1×7) = k^(−6−7) = −13k^Nm. Magnitude = 13Nm. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 13 Nm. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

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

A 3kg particle moves with velocity v\=6i^−4j^m/s at r\=2j^m. What is the z-component of its angular momentum?

L = r×p = |i^j^k^0206−40| = k^(0×(−4)−2×6) = −12k^kg m2/s. Z-component = −12kg m2/s. As per NCERT, applying relevant law/formula with correct units and sign convention leads to -12 kg m²/s. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

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

A torque of 25Nm acts on a wheel with moment of inertia 5kg m2 starting from rest. What is its angular speed after 2s?

α = τI = 255 = 5rad/s2. ω = ω0+αt = 0+5×2 = 10rad/s. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 10 rad/s. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

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