A horizontal platform is rotating with uniform angular velcity 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 :

Options

A. decreases continously
B. remains unltered
C. decreases initially and increases again
D. increases continuously

Answer

C

Explanation

( c) From law of conservation of angular momentum if no external torque is acting upon a body rotating about an axis, then the angular momentum of the body remains constant that is
`J = I omega = constant`
Hence, if decreases, `omega` increases and vice-versa. When liquid is dropped, mass increase hence `I` increases `(I = mr^2)` So, `omega` decreases, but as soon as the liquid starts falling `omega` increases again.