Activity 3: Take a depth breath! Directions: Answer the following word problems by applying what you have learned in the lesson. Show your complete solution by following the G-R-E-S-A format. Problem 1. Pressure Pressure at a Faucet. The surface of the water in a storage tank is 30 m above a water faucet in the kitchen of a house, Fig. Calculate the difference in water pressure between the faucet and the surface of the water in the tank. The density of the water is 1x103 4 Figure 18. Pressure at a Faucet Ah = 30 m Photo Credit: Giancoli Physics 6th Approach - Water is practically incompressible, so p is constant even for a Ah = 30 when used in equation AP = pg Ah. Only Ah matters; we can ignore the "route" of the pipe and its bends. Note: The height h is sometimes called the pressure head. In the figure, the head of water is 30 m at the faucet. The very different diameters of the tank and faucet don't affect the result - only pressure does. Problem 2. Fluids at Rest What Force Must a Dam Withstand? Consider the pressure and force acting on the dam retaining a reservoir of water. Suppose the dam is 800 m wide and the water is 120.0 m deep at the dam. (a) What is the average pressure on the dam due to the water? (b) Calculate the force exerted against the dam? Figure 19. Pressure at a Faucet Photo Credit: Giancoli Physics 6th F = PA p = hpg F The average pressure p due to the weight of the water is the pressure at the average depth h of 60.0 m, since pressure increases linearly with depth. The force exerted on the dam by the water is the average pressure times the area of contact, F = PA