24. (a) At depth ythe gauge pressure of the water is p= ρgy, where is the density of the water. We consider a horizontal strip of width Wat depth y, with (vertical) thickness dy,across the dam. Its area is dA= W dyand the force it exerts on the dam is dF= p dA= gyW dy. The total force of the water on the dam is ()()2233209111.00 10 kg m9.80m s314m 35.0m221.88 10 N.DFgyW dygWDρρ===×=×³(b) Again we consider the strip of water at depth y. Its moment arm for the torque it exerts about
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