2. The gate AB shown in the figure is rectangular with a length Z and width w into the page. The gate has a frictionless hinge at point A and it is held against a stop at point B by a weight mg; the pulley redirecting the weight's cable is also frictionless. Neglecting the weight of the gate, derive an expression for the water height h at which the gate will start to move away from the stop. h B Patm mg water, density p gate Patm