A quarter circle (10 m diameter) gate which is 10 m wide perpendicular to the paper holds water as shown in the figure. Find the force required to hold the gate. The weight of the gate can be neglected.

Horizontal force

And it acts at a distance of 5/3 m from the bottom end.

And the upward vertical force is the weight of the imaginary water body held over the plate.
                  
And it will act through its C.G. which is Determined as follow -
               
C.G. of total area about AA is 2.5m away from AA.

Distance from 'O'= (5-3.88) = 1.12m.
Taking moments about  
Answer:-