Density of liquid is d
You can calculate the total force on the container from the pressure by integrating the pressure over the height of the container as follows:
In this case, the area element dA will be equal to a differential height element dh times the circumference of the rectangle 2*(Len +breadth) ,which gives
You can note that since the pressure is linear in height, you get average pressure by taking the pressure to be at the mid-point of the tank. Therefore Torque
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