A horizontal platform is rotating with uniform angular velocity a… - Vidyadip

MCQ

A horizontal platform is rotating with uniform angular velocity around the vertical axis passing through its centre. At some instant of time a viscous fluid of mass $m$ is dropped at the centre and is allowed to spread out and finally fall. The angular velocity during this period

A
decreases continuously
✓
decreases initially and increases again
C
remains unaltered
D
increases continuously

✓

Answer

Correct option: B.

decreases initially and increases again

b
When the fluid spreads out, the moment of inertia of the system is increased. If we apply conservation of angular momentum

$I\omega = {I_1}{\omega _1}$

As $I$ increases due to water spreading out, the angular velocity decrease. When water level falls, $I$ decreases resulting in increased angular velocity

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