Answer:
29.76245 rad/s², -117.80972 rad/s²
28.2743 rad/s
3.95833
Explanation:
= Final angular velocity
= Initial angular velocity
= Angular acceleration
= Angle of rotation
t = Time taken
Equation of rotational motion

Angular acceleration during speed up is 29.76245 rad/s²

Angular acceleration during spin down is -117.80972 rad/s²
Angular speed is given by

Maximum angular speed reached by the flywheel is 28.2743 rad/s


The ratio would be 
1 kilogram = 1,000 grams
1 kilogram = 1,000,000 milligrams
KE = (1/2) (mass) (speed)²
KE = (1/2) (0.5 kg) (10 m/s)²
KE = (1/2) (0.5 kg) (100 m²/s²)
KE = (0.25 kg) (100 m²/s²)
KE = 25 Joules