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togo

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## Homework Statement

Compute the torsional shear stress and angle of twist in degrees in an aluminum tube, 600 mm long, having an inside diameter of 60 mm and outside diameter of 80 mm when subjected to a steady torque of 4500 N*m. Then specify a suitable aluminum alloy for tube.

## Homework Equations

angle = TL/GJ

J = piD^4/32 (Do^4 - Di^4)

## The Attempt at a Solution

angle = (4500 N*m)(0.6 m) / (2.8 x 10^-6)(80 x 10^9) = 0.012 rad

Book answer: 0.0378 rad

Wrong answer obviously. Why? Thanks