A thin horizontal circular disc is roating about a vertical axis passing through its centre. An insect is at rest at a point near the rim of the disc. The insect now moves along a diameter of the disc to reach its other end. During the journey of the insect, the angular speed of the disc.

Options

A. continuously decreases
B. continuously increases
C. first increases and then decreases
D. remain unchanged

Answer

C

Explanation

As external torque is zero, i.e. `tau = 0`, so angular momentum is conserved.
`:. I omega = a` constant `= C`
or `omega = (C )/(I) or omega prop (1)/(I)`
When insect moves towards centre `I `decrease. Hence `omega` increases. As insect moves away from centre towards diametrically opposite point, `I` increases. Then `omega` decreases. Thus `omega` first increases and then decrease.