The face of a 100m wide rectangular dam is built at an angle of 60 degrees above the horizontal and holds back a body of fresh water that is 30m deep at the face of the dam. Assuming hydrostatic conditions, what angle would be needed in order for an equivalent body of salt water to exert the same force on the dam? Assume the density of fresh water to be 1000kg/m^3 and the density of salt water to be 1030kg/m^3 .