A thin horizontal circular disc is rotating about a vertical axis… - Vidyadip

MCQ

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

A
Continuously decreases
B
Continuously increases
✓
First increases and then decreases
D
Remains unchanged

✓

Answer

Correct option: C.

First increases and then decreases

c
Moment of inertia of the insect disc system,

$M I=\frac{1}{2} M R^{2}+m x^{2}$

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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