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Question:

A thin horizontal circular disc is rotating about a vertical axis passing through its center. 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

remains unchanged

first increases and then decreases

Solution:

Angular momentum L = Iω
L = mr2 × ω
Since r first decreases then increases.
So, due to conservation of angular momentum, L first increases then decreases.