A closed tank rectangular in plane with vertical sides is 1.8m deep and contains water to a depth of 1.2m.
Air is pumped into the space above the water until the air pressure is 35kN/m2.
If the length of one wall of the tank is 3m, determine the resultant force on this wall and the height of the centre of pressure above the base.
So far my calculations have been to calculate the pressure due to the water which is: rho(g)(h) = 1000(9.81)(1.2) = 11,772 N/m^2. I then multiply this by the arc of the side of the tank covered by water which is: 1.2(3) = 3.6m^2.
Multiplying these gives 42379.2N.
I am not entirely sure what to do with the air pressure. Whether to multiply it again by 3.6 (the area of the side of the tank covered by water) or to multiply it by the area of the top of the water but I would not have enough details to calculate this.