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http://img206.imageshack.us/img206/6093/problem1rm4.th.png [Broken]

Isn't the shear stress for both the inner and outer negative? When i take the derivative i get negative. The derivative is basically ln ( 1/x) since the rest are just constants.

Edit: I meant that the expression looks similar to ln (1/x).

Also I am clueless to how they got the values for that the velocity destribution graph. They picked a/b = 0.8 and i believe the # has to be less than 1 or the Vz equation is undefined.

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# Fluid Mechanics question (shear stress)

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