A thin horizontal circular disc is rotating about a vertical axis passing through its centre. An insect is at rest at a point near the rim of the disc - Physics MCQ FIITJEE AIEEE 2011 (Set Q) 2026 | ExamTest.live

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A thin horizontal circular disc is rotating about a vertical axis passing through its centre. An insect is at rest at a point near the rim of the disc. The insect now moves along a diameter of the disc to reach its other end. During the journey of the insect, the angular speed of the disc:

Solution & Step-by-step Explanation

By conservation of angular momentum (L = I ω = constant):As the insect moves from the rim towards the centre, the moment of inertia (I) of the system decreases (since I = I_{disc} + m r^{2} and r decreases). Consequently, the angular speed ω increases.As the insect moves from the centre towards the other end of the rim, r increases, I increases, and ω decreases.Therefore, the angular speed first increases and then decreases.

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A thin horizontal circular disc is rotating about a vertical axis passing through its centre. An insect is at rest at a point near the rim of the disc. The insect now moves along a diameter of the disc to reach its other end. During the journey of the insect, the angular speed of the disc:

continuously decreases

continuously increases

first increases and then decreases

remains unchanged

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