please show all steps and equations to solve this problem.$(30$ points$)$ A metal disc is falling in a circular cylinder, open at the top and filled with water. The

diameter of the cylinder is $D$ and the disc is falling with a velocity $V_0.$ The diameter of the disc is

$D,$ where Determine the average velocity of the fluid moving upwards between the disc

and the sides of the cylinder, $U_{\text{a}\text{v}\text{g}\text{.}}.$ The thickness of the disc is $H.$