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I have an aluminium disc of 300mm diameter and 8mm thick and a mass of 1.58Kg. To work out the inertia I have used the formula:

I = 0.5m*r^2

I= 0.79*0.0225

I= 0.0178 Kg m^2

Now, the disc is to spin at 30rpm (0.25 secs to move 45 degrees) and I would like to find the torque, so I calculate:

angular velocity ω1= 0

angular velocity ω2= ((30rpm/60)*2pi) = 3.1415 rad/s

α = (ω2-ω1)/t = (3.1415-0)/0.25 = 12.57 rad/s^2

T= Iα = 0.0178*12.57 = 0.2237 Nm

How close am I, or have I gone wrong somewhere?

Also, does anyone know if the formula below is correct:

M = (Jω)/t

Thanks in advance.