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## Homework Statement

A 250 g , 20.0-cm-diameter plastic disk is spun on an axle through its center by an electric motor.

## Homework Equations

What torque must the motor supply to take the disk from 0 to 2000 rpm in 4.50 s?

## The Attempt at a Solution

I know that Torque = Inertia times angular acceleration or T = Ia.

I tried using the formula for inertia of a solid disk, I = 1/2Mr^2. So with that I get 1/2(.25)(.1^2) = .00125. Then i found angular acceleration: 2000 rpm = 209.44 rad/s divided by 4.5 s so 209.44 rad/s / 4.5s = 46.54 s^2. I multiply these two number together and get .00125*46.54 = .06 Nm. However, this is wrong. What am I doing wrong?