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Question #42249

Difficulty: 8/10 | 🟢 Free

The Question

A gyroscope consists of a uniform solid disk of mass M=2 kgM = 2 \text{ kg} and radius R=0.1 mR = 0.1 \text{ m} mounted on a massless axle. The axle is attached to a frictionless pivot on the vertical axis of a rotating platform. The distance from the pivot to the center of mass of the disk is L=0.2 mL = 0.2 \text{ m}. The platform rotates at a constant angular velocity Ω=10 rad/s\Omega = 10 \text{ rad/s} about the vertical axis. The gyroscope axle is observed to maintain a steady angle θ=60∘\theta = 60^\circ with the upward vertical, precessing together with the platform. Calculate the required spin angular velocity ω\omega of the disk about its axle. (Take g=10 m/s2g = 10 \text{ m/s}^2)

Options

  • A.

    77.5 \text{ rad/s}

  • B.

    40.0 \text{ rad/s}

  • C.

    75.0 \text{ rad/s}

  • D.

    2.5 \text{ rad/s}

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Intuition_Breaker

Train your brain to resist "obvious" answers that are designed to deceive your intuition.

Concepts Behind This Question

Frame of Reference Dependency|Gyroscopic Stability|Vector Cross-Products

Why This Question Is Tricky

Common Mistakes

This question exposes the 'Lethal Collision' of blindly applying the standard simplified gyroscopic precession formula (Ω=τ/Isω\Omega = \tau / I_s \omega) in a non-inertial setup.

Students often ignore the vector addition of the platform's angular velocity to the gyroscope's spin, which alters the total angular momentum vector.

Consequently, they miss the Ω2\Omega^2 terms that arise from the cross product Ω⃗×L⃗\vec{\Omega} \times \vec{L} (physically manifesting as centrifugal torque and Coriolis effects on the extended rigid body).

Failing to account for the transverse moment of inertia I⊥I_\perp and these fictitious torques leads directly to the trap answer of 40.0 rad/s40.0 \text{ rad/s}.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterSystem of Particles and Rotational Motion - Class 11 Part 1
ConceptGyroscopic Stability
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree