ism_ch15 - Chapter 15 Fluids Answers to Even-numbered...

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315 Chapter 15 Fluids Answers to Even-numbered Conceptual Questions 2. No, because the Moon has no atmosphere to press down on the surface of the liquid. 4. A suction cup is held in place by atmospheric pressure. When the cup is applied, you push it flat against the surface you want to stick it to. This expels most of the air in the cup, and leads to a larger pressure on the outside of the cup. Thus, atmospheric pressure pushes the outside of the cup against the surface. 6. The balloon moves toward the front of the car. The reason is that as the car accelerates forward, the air inside it shifts toward the rear of the car – just as passengers are pressed back into their seats. This makes the pressure of the air in the car increase as one mores from front to back. The helium-filled balloon moves in the direction of decreasing pressure – like any buoyant object – which in this case is toward the front of the car. 8. Mercury is more practical in a barometer than water because of its greater density. With such a large density, the height of the mercury column is only about 0.760 m. The density of water is less than that of mercury by roughly a factor of 14. Therefore, the height of a water column in a barometer would be about 10 m – the height of a three-story building. 10. In a hot-air balloon, vertical motion is controlled by adding heat to the air in the balloon, or by letting it cool off. As the temperature of the air in the balloon changes, so too does its density. By controlling the overall density of the balloon, one can control whether it rises, falls, or is neutrally buoyant. 12. Whether the block is upright or inverted, its weight is the same. Therefore, the volume of water that must be displaced to float the block is the same in either orientation. As a result, the water level in the tank remains the same. 14. The total mass contained in the flask is the same before and after the string breaks. It follows that the reading on the scale will be the same. 16. The physics in this case is pretty “ugly”. Ice floats in water, whether it is a house-sized iceberg, a car-sized chunk, or a thimble-sized ice cube. If the Earth is warming and icebergs are breaking up into smaller pieces, each of the smaller pieces will be just as buoyant as the original berg. 18. (a) The boat is now carrying a reduced weight. Therefore, it floats higher relative to the water. (b) The water level in the pool remains the same because the blocks of wood displace the same amount of water whether they are in the boat or in the water. In either case, they displace a volume of water with a weight equal to their weight. 20. The problem is that as you go deeper into the water, the pressure pushing against your chest and lungs increases rapidly. Even if you had a long tube on your snorkel, you would find it difficult to expand your lungs to take a breath. The air coming through the snorkel would be at atmospheric pressure, but the water pushing against your chest might have twice that pressure. Thus, scuba gear not only holds air for you in a tank, but feeds it to you under pressure.
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This note was uploaded on 04/07/2008 for the course PHYS 105 taught by Professor Klie during the Spring '08 term at Ill. Chicago.

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ism_ch15 - Chapter 15 Fluids Answers to Even-numbered...

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