A 4-m-long quarter-circular gate of radius 2m and of negligible weight is hinged about its upper edge A, as shown in the figure. The gate controls the flow of water over the ledge at B, where the gate is pressed by a spring. Determine the minimum spring force required to keep the gate closed when the water level rises to A at the upper edge of the gate. Take the density of water to be 1000kg/m3. The minimum spring force required to keep the gate closed is kN