Answer:
The angular momentum and angular velocity are 1.134 kg.m²/s and 174.5 rad/s.
Step-by-step explanation:
Given that,
Moment of inertia

Torque = 21 N.m
Time dt = 54 ms
(a). We need to calculate the angular momentum
Using formula of torque


Where, dL = angular momentum
t = time
= torque
Put the value into the formula


(b). We need to calculate the angular velocity of the disk
Using formula of angular velocity




Hence, The angular momentum and angular velocity are 1.134 kg.m²/s and 174.5 rad/s.