An isosceles triangular plate of base 3m and altitude 3m is immersed in oil vertically with its base coinciding with the free surface of the oil of relative density 0.8. Determine the total thrust.

Area of the plate = $4.5m^2$ , density of the oil =  $0.8\times 1000=800kg-m^{-3}$
Depth of the C.G of the plate from free surface is $\frac{1}{3}.3=1m$
Now the total thrust on the plate = ( plate area ).( pressure at the C.G of the plate) =  $4.5\times (800\times 10\times 1)=36kN$