Question

A horizontal platform is rotating with uniform angular velocity around the vertical axis passing through it 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
• B. decrease initially and increases again
• C. remains unaltered
• D. increases continuously

Answer 1

Answer: (B)

decrease initially and increases again

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.