Question

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

(a) Decreases continuously

(b) Decreases initially and increases again

(c) Remains unaltered

(d) Increases continuously

I have been asked this question in exam.

My question is based upon Significance of Moment of Inertia in portion Laws of Motion of Engineering Physics I

Answer 1

The correct option is (b) Decreases initially and increases again

For explanation I would say: By conservation of angular momentum,

L = Iω = constant

As the liquid is dropped, it starts spreading out. The moment of inertia increases and angular velocity decreases. As the liquid starts falling, the moment of inertia again decreases and the angular velocity increase.