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STD 11 - 6. system of particles and rotational motion — JEE STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceJEESTD 11 - 6. system of particles and rotational motion4 Marks
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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