A gate as shown in fig, is hinged at O and it is in the form of a quadrant of a circle of radius 1m. It supports water at one side. If the length of gate is 3.5m find the force required to hold the gate.

Horizontal force component

  Where A is the projected area =3.5 x1=3.5m²

And it acts at a distance 1 / 3 m from hinge

The vertical force is the weight of the water held

Acting through the centroid of the water held and is located at 4p / 3 m from the vertical line through A.
Now, taking moments about the hinge we get    

Answer:- 17.16 kN.