$2.[20$ points$]$ A two$-$dimensional flow is described by circular streamlines $($vr $=0$ and v $6=0)$ in the xy plane. The y component of the velocity is v $=5$x$.[$Hints: this is NOT a free$-$vortex flow. If vr $=0,$ using the relationship between Cartesian and cylindrical coordinates, we have u $=$v $$ sin $,$ and v $=$ v $$ cos $.]($a$)$ Determine the x component of the velocity $($u$).($b$)$ Is the flow incompressible? Explain. $($c$)$ Is the flow irrotational? Explain. $($d$)$ Determine the corresponding stream function.