A 680 kg disk of radius 1.2 m is mounted on a fixed axle. A force exerted on the

Question

A 680 kg disk of radius 1.2 m is mounted on a fixed axle. A force exerted on the disk causes a constant torque that gives the disk a rotational acceleration magnitude of 0.30 s^-2 for 5.0 s. If the disk had an initial rotational speed of 4.5 s^-1, how much work was done to provide the torque, assuming no energy is lost to friction?   
A 680 kg disk of radius 1.2 m is mounted on a fixed axle. A force exerted on the disk causes a constant torque that gives the disk a rotational acceleration magnitude of 0.30 s^-2 for 5.0 s. If the disk had an initial rotational speed of 4.5 s^-1, how much work was done to provide the torque, assuming no energy is lost to friction?   

Explanation / Answer

moment of inertai of the disk = 0.5MR^2 = 0.5*680*1.2^2 = 489.6 kg-m^2

Torque = I (alpha) = 489.6*0.3 = 146.88 N-m

angular displacement , theta = 4.5*5+ (0.5*0.3*5^2) = 26.25 rad

work done = Torque * theta = 146.88*26.25 = 3855.6 J

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