Q.

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 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 [AIIMS 2018] 

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a

first increases and then decreases

b

continuously increases

c

continuously decreases

d

remains unchanged

answer is C.

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Detailed Solution

remains unchanged

MI=12MR2+mx2

where, m = mass of insect
and x = distance of insect from centre.
Clearly, as the insect moves along the diameter of the disc.
Moment of inertia first decreases and then increases.
By conservation of angular momentum, angular speed first increases and then decreases.

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