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A 1.5m-diameter floodgate placed vertically is 6m below the water level at it's

highest point. The gate is hinged at the top and opens into the

reservoir. Calculate the required horizontal force applied at the bottom of the gate

in order to open it when the pressure on the other side of the gate in the outflow

pipe is sub-atmospheric at -5m gauge pressure head.

The equations I used are:

F = ρgh

_{g}A to calculate the magnitude of the force acting on the outside of the gate

h

_{p}= [(I

_{G})/(h

_{g}A)]+h

_{g}to calculate at what depth the force acts.

I am able to calculate the force acting on the reservoir side of the gate to be 34.65KN and also where it acts to be 4.51m, using the above equations. After that however i'm lost. I know I probably have to take moments around the hinge using the above data to eventually calculate the required force but I'm not quite sure as how to go about that.

Any help would be greatly appreciated :)