The angular momentum of a flywheel

[Eggyu]

The angular momentum of a flywheel having a rotational inertia of 0.200 kg·m2 about its axis decreases from 3.00 to 1.800 kg·m2/s in 1.80 s.

(a) What is the average torque acting on the flywheel about its central axis during this period?
N·m
(b) Assuming a uniform angular acceleration, through what angle will the flywheel have turned?
rad
(c) How much work was done on the wheel?
J
(d) What is the average power of the flywheel?
W

Basically, all i need is how to find the initial angular velocity for part b. The rest of the variables i have solved for.

 

[andrevdh]

The angular momentum of a rigid object about a fixed axis is given by

L = I\omega

where I is its moment of inertia bout this axis and \omega is its angular speed about the same axis.

 

[Bill Foster]

The rotational components and equations are analogous to linear ones.

Equation of motion:

linear:
(1) x=x_0+vt+\frac{1}{2}at^2
(2) v=v_0+at
(3) F=ma
(4) W=Fx
(5) P=Fv
(6) a(x-x_0)=\frac{1}{2}(v^2-v_0^2)

angular:

(1) \phi=\phi_0+\omega t+\frac{1}{2}\alpha t^2
(2) \omega=\omega_0+\alpha t
(3) \tau=I\alpha
(4) W=\tau \phi
(5) P=\tau \omega
(6) \alpha(\phi-\phi_0)=\frac{1}{2}(\omega^2-\omega_0^2)

So to find the average torque in part (a), find the deceleration using angular equation 2.

Part (b), use 6.

Part (c), use 4.

Part (d), use 5.