A flushing tank has an $L-$shape gate at its bottom corner and hinged at $O$ as depicted

in Fig. B The vertical leaf of the gate is $500mm$ by $400mm$ and the horizontal

leaf is $400mm$ by $400mm.$ Water is continuously filled into the tank. Determine

the depth of water, $h,$ that will cause the gate to turn clockwise and to discharge

the water.

Fig. B