Submerged Gates: Example Problems

Try to solve these problems before watching the solutions in the screencasts.

Example Problem 1

A door (3 ft tall and 2 feet wide) is located in the side of a tank and is hinged along its bottom edge.  A pressure of 100 lbf/ft2 is applied to the liquid free surface of the tank, and the top of the liquid free surface aligns with the top of the submerged door.  Find the force required to keep the door closed.  The specific weight of the liquid is 100 lbf/ft3.

Example Problem 2

A gate supports a channel of water on its left side, and has a hinge at the bottom of the gate.  The height of the gate and water is “a” meters and extends “b” meters into the page.  The top of the water and the right side of the gate are both exposed to atmospheric pressure.  Derive an equation for the moment at the hinge needed to keep the gate closed.