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Unformatted text preview: 983 Chapter 13 Fluids Conceptual Problems 1 • Determine the Concept The absolute pressure is related to the gauge pressure according to P = P gauge + P at . While doubling the gauge pressure will increase the absolute pressure, we do not have enough information to say what the resulting absolute pressure will be. ( ) correct. is e *2 • Determine the Concept No. In an environment where 2 g eff = − = r v m F g , there is no buoyant force; there is no ″ up ″ or ″ down. ″ 3 •• Determine the Concept As you lower the rock into the water, the upward force you exert on the rock plus the upward buoyant force on the rock balance its weight. When the thread breaks, there will be an additional downward force on the scale equal to the buoyant force on the rock (the water exerts the upward buoyant force on the rock and the reaction force is the force the rock exerts on the water … and hence on the scale). Let ρ represent the density of the water, V the volume of the rock, and w f the weight of the displaced water. Then the density of the rock is 3 ρ . We can use Archimedes’ principle to find the additional force on the scale. Apply Archimedes’ principle to the rock: g V g m w B f f f f ρ = = = Because V f = V rock : Mg g M g M B 3 1 rock 3 = = = ρ ρ ρ ρ and correct. is ) ( d 4 •• Determine the Concept The density of water increases with depth and the buoyant force on the rock equals the weight of the displaced water. Because the weight of the displaced water depends on the density of the water, it follows that the buoyant force on the rock increases as it sinks. correct. is ) ( b 5 •• Determine the Concept Nothing. The fish is in neutral buoyancy (that is, its density equals that water), so the upward acceleration of the fish is balanced by the downward Chapter 13 984 acceleration of the displaced water. *6 •• Determine the Concept Yes. Because the volumes of the two objects are equal, the downward force on each side is reduced by the same amount when they are submerged, not in proportion to their masses. That is, if m 1 L 1 = m 2 L 2 and L 1 ≠ L 2 , then ( m 1 − c ) L 1 ≠ ( m 2 − c ) L 2 . 7 •• Determine the Concept The buoyant forces acting on these submerged objects are equal to the weight of the water each displaces. The weight of the displaced water, in turn, is directly proportional to the volume of the submerged object. Because ρ Pb > ρ Cu , the volume of the copper must be greater than that of the lead and, hence, the buoyant force on the copper is greater than that on the lead. correct. is ) ( b 8 •• Determine the Concept The buoyant forces acting on these submerged objects are equal to the weight of the water each displaces. The weight of the displaced water, in turn, is directly proportional to the volume of the submerged object. Because their volumes are the same, the buoyant forces on them must be the same. correct. is ) ( c 9 • Determine the Concept It blows over the ball, reducing the pressure above the ball to...
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- Spring '10
- Buoyancy, numerical values