Question 4: Centre of Mass and Rotational Motion

Question

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

Accepted Answer

Moment of inertia of the insect disc system,
$$\mathrm{MI}=\frac{1}{2} M R^2+m x^2$$
where, $$m=$$ mass of insect
and $$\quad x=$$ 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.

Answer

continuously decreases

Answer

continuously increases

Answer

first increases and then decreases

Answer

remains unchanged

Centre of Mass and Rotational Motion

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

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