Determine the shear-stress variation over the cross
section of the thin-walled tube as a function of elevation y and
show that tmax = 2V >A , where A = 2prt. Hint: Choose a
differential area element dA = Rt du . Using dQ = y dA,
formulate Q for a circular section from u to (p - u) and
show that Q = 2R2t cos u, where cos u = 2R2 - y2 >R.