The correct option is
D First increase and then decrease.
⇒The external force on system is weight of disc, which passes through it's centre and weight of insect
mg is parallel to axis of rotation, so
τext=0, hence angular momentum will be conserved for system.
Li=Lf
From the shown figure, as the insect crawl on the diameteric line towards the axis of rotation, it's distance from axis decreases and in next half as it crosses then distance from centre (
r) increases
The angular momentum of insect is given by
L;
L=Iω
L=mr2ω
Since,
r first decreases then increases.
⇒ For insect,
L decreases first, then increases.
∴ To conserve system's angular momentum, angular speed of disc (
ω) will increase first, then decreases.