The horizontal velocity in the wake behind an object in an air stream of velocity \(U\) is given by

\[\begin{array}{ll} u(r)=U\left[1-\cos ^{2}\left(\frac{\pi r}{2}\right)\right] & |r| \leq 1 \\ u(r)=U & |r|>1 \end{array}\]

where \(r\) is the nondimensional radial coordinate, measured perpendicular to the flow. Find an expression for the drag on the object.