The diagram shows a rigid gate (OAB), which is hinged at O and rests against a rigid support at B. Calculate the minimum horizontal force, P,...

The diagram shows a rigid gate (OAB), which is hinged at O and rests against a rigid support at B. Calculate the minimum horizontal force, P, required to keep the gate closed if its width is 3 m. Neglect the weight of the gate and friction in the hinge. The back of the gate is exposed to the atmosphere.