A circular platform is free to rotate in a horizontal plane about a vertical axis passing through its center. A tortoise is sitting at the edge of the platform. Now, the platform is given an angular velocity c.o0. When the tortoise moves along the diameter of the platform with a constant velocity (with respect to the platform), the angular velocity of the platform `omega`(t) will vary with time t as

Options

A.
B.
C.
D.

Answer

B

Explanation

As the tortoise approaches the centre of the disk, the moment of inertia of disk + tortoise system decreases. As there is no external torque on this system, angular momentum remains conserved.
`I_(i)W_(i) = I_(F)omega_(F)`, hence `omega` increases.
Once the tortoise reaches the centre `omega` becomes maximum (since moment of inertia is minimum). Then the moment of inertia again starts increasing (as tortoise moves away from the centre).