Question

1.1
Q159
A horizontal platform is rotating with a uniform
angular velocity around a vertical axis passing
through the centre At a certain 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 :
(1) decreases continuously
(2) decreases initially and increases again
(3) remains unaltered
(4) increases continuously. what is the correct answer​

Answer 1

Explanation:

As there is no external torque present here,the angular momentum is conserved.

or, Angular momentum=(moment of inertia)*(angular velocity)=constant

So,as liquid got spread out mass getting farther from center increases the overall moment of inertia.Hence the decrease in angular velocity first ,but then liquid falling through perimeter of disk again decreases the moment of inertia until it become same as before as before pouring of liquid.Thus the angular velocity increases for that time to be the previous value.

Therefore the decrease initially & then increase again in the value of angular velocity.