C$.$ Consider a door of length $L$ and width $($into the page$),W$ that is keeping the liquid of

density $$ in the tank.

a$.$ What should be the minimum mass, $M$ of the door from keeping the liquid in the

tank$?($Assume that there is good gasket around the door to keep things liquid$-$tight$).$

Hint: note there is a hinge so you need to consider toque balance.

b$.$ If the door is made of solid steel $($density $7\mathrm{.}5\frac{g}{c}{m}^3),H=2m$ and $L=4m,$ what

would be the minimum thickness of the door?

Liquid density:

$$