Oil flows between two parallel plates, one of which is at rest and the other moves with a velocity U $,($a$)$ If the pressure is decreasing in the direction of flow at the rate of $5$ Pa$/$m$,$ the dynamic viscosity is $0\mathrm{.}05$ kg$/$ms$,$ the spacing of the horizontal plate is $0\mathrm{.}04$ m and the volumetric flow & per unit width is $0\mathrm{.}02$ m$\text{'}$s$,$ what is the velocity U$?($b$)$ Calculate U if the pressure is increasing at a rate of $5$Pa$/$m in direction of flow