The force on a submerged gate is due to hydrostatic pressure, which increases linearly with depth. The gate is 1m×1m, hinged at its midpoint. The average pressure on the left side acts at the centroid of the submerged area. The hydrostatic force is $F=\rho g\overline{h}A$, where $\overline{h}$ is the centroid's depth. For this square, the centroid is at 0.5m from the top. The area A=1m². Thus, $F=\rho g\times 0.5\times 1=\frac{\rho g}{2}$. The hinge is at the midpoint, so the moment arm is zero, meaning no additional force is needed to hold it stationary beyond countering the fluid force. Therefore, the required force is 1/2 ρg.

Final Answer: 1/2 ρg