1. The problem statement, all variables and given/known data The rectangular gate shown in section is 3 m long (perpendicular to the paper) and is hinged about its upper edge B. The gate divides a channel leading to a fresh-water lake on the left and a salt-water tidal basin on the right. Calculate the moment, M, on the shaft of the gate at H required to prevent the gate from opening when the salt-water level drops to h = 1 m. Take the density of salt water 1050 kg/m3 2. Relevant equations 1. Force=rho*g*v 2. F=gamma*h*a 3.R= rho*g*h*a Where gamma = specific weight of liquid Where R=hydrostatic pressure 3. The attempt at a solution Calculate Both forces acting on rectangle gate. Then solve for the moment Using sum of moments **** I am confused on which equation to use. I want to use 3. since its a flat surface but I confused whether to use gravity in the equation?