Physics Frictional Torque Problem?

Hello

if the wheel turns counterclockwise, the angular velocity vector comes out of the plane (up) in direction of the axis.

The angular deceleration α is 60 rad/s in 300 s = 60/300 rad/s^2 = 0,2 rad/s^2.

and the moment of inertia = 1/2*mr^2 = 200*3^2 = 1800 kgm^2.

And frictional torque acting is τ = I*α = 1800*0,2 = 360 Nm

Regards

B) Calculate the frictional torque acting on the flywheel.

torque acting = change in angular momentum/time

angular momentum = inertia x omega (rad/s)

inertia = 1/2mr^2 = 0.5 x 400 x 3^2 = 1800 kg.m^2

Initial momentum = 1800 x 90 = 162000 kg.m^2/s

final momentum = 1800 x 30 = 54000 kg.m^2/s

change in momentum = 54000 - 162000 = - 108000 kg.m^2/s

-108000/300 = - 360 Nm