1. A pipe has circular cross section of radius ro. Water is flowing in the pipe. At the pipe exit, the velocity is only in the x-direction, but it varies

with r according to: \boldsymbol{u}(\boldsymbol{r})=U\left[1-\frac{\boldsymbol{r}^{2}}{\boldsymbol{\tau}_{0}^{2}}\right] If U = 2 m/s and ro = 10 cm, find the mass flow rate of water in the pipe.