The velocity profile for fully developed laminar flow in a circular tube is \(u=u_{\max }\left[1-(r / R)^{2}\right]\). Obtain an expression for the shear force per unit volume in the \(x\) direction for this flow. Evaluate its maximum value for a pipe radius of \(75 \mathrm{~mm}\) and a maximum velocity of \(3 \mathrm{~m} / \mathrm{s}\).