Question

spinning disk of mass 5.0 kg and radius 0.25m is rotating about an axis through its center at 400 rev/min. a.) What is the angular velocity of the disk in rad/s? b.) What is the moment of inertia of the disk? c.) If it accelerates at a constant rate to 800 rev/min in 8 sec, what is its angular acceleration? d.) What constant torque is required to produce this acceleration? e.) When it reaches that speed, what is its kinetic energy? f.) When it reaches that speed, what is its angular momentum?

Answer 1

Hey ash
400 rpm means 400/60 revolutions per second
each revolution corresponds to an angle of 2 pi
so angular velocity is 2 *pi* 400/60
Moment of inertia is 1/2 m * r *r for disk
if acceleration is constant (say a) then the change in angular velocity in eight seconds should be 8*a which should be the difference in the final and initial angular velocity
so you can get the angular acceleration
now torque=moment of inertia *angular acceleration
Hope this helps! :)