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NEET PHYSICSRotational motionMedium

Question

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 mm is dropped at the centre and is allowed to spread out and finally fall. The angular velocity during this period:

A

Decreases continuously

B

Decreases initially and increases again

C

Remains unaltered

D

Increases continuously

Step-by-Step Solution

When the viscous fluid is dropped at the center, it starts spreading outwards towards the edge of the platform. As the fluid spreads, its distance rr from the axis of rotation increases, which increases the total moment of inertia (II) of the system (since Imr2I \propto mr^2). According to the law of conservation of angular momentum (L=Iω=constantL = I\omega = \text{constant}), an increase in the moment of inertia results in a continuous decrease in the angular velocity (ω\omega). When the fluid finally falls off the edge, it carries away its corresponding angular momentum. At this point, the platform continues to rotate with the constant reduced angular velocity it had just before the fluid fell. Therefore, the angular velocity does not increase again, but rather decreases continuously while the fluid is spreading.

Exam Context & Concepts Covered

This question aligns with the NEET PHYSICS syllabus, specifically targeting concepts from Rotational motion. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

PHYSICSRotational motionhorizontalplatformrotatinguniformangular

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