Your Answer to Q30. Sorry, your answer is not correct. Remember sound is a pressure wave in air.
Help: Fundamentals of Sound, Sec. 1-J.
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Your Answer to Q30. Congratulations, your answer is correct.
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Hint for Question 30: Sound travels through the air as a pressure or density wave, but it can travel in solids as well as air.
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Correct Answer to Question 30: Sound is a vibration of the air molecules such that the density and pressure changes are carried along as a wave. When the sound wave hits the wall, it compresses (or rarefies) slightly the molecules in the wall and sound travels in the solid material of the wall. Sometimes the material of a wall, if thin enough, does not compress but just bends in and out so that it compresses the air on the opposite side transferring the sound wave through the wall in that fashion. In either case the sound has been transmitted through the wall and c) is the correct answer.
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Your Answer to Q33. Sorry, your answer is not correct.
Help: Fundamentals of Sound, Sec. 1-I.
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33
Hint
for Question 33: The pressure of the atmosphere in about 14.7 pounds per
square inch on each part of our bodies. That is actually quite a large force
by human standards. It has to be counteracted by some other force. Think of
the easiest way nature might provide this.
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Correct
Answer to Question 33: A submarine withstands the crush of very deep water
by having a hull that is strong enough to resist that force of external water
pressure . (The force of water pressure gets greater as one goes deeper in the
ocean. Think of the weight of a large column of water right over the submarine
pushing down on it.) However, the cells of our bodies are not strong like a
submarine hull. The external pressure of the air is overcome simply by having
gases of air, nitrogen and oxygen, dissolved in the liquids of our bodies. Thus
those gases press back resisting the crushing forces of air pressure. If you
were to be exposed to the vacuum of space, without a space suit, these gases
would expand quickly —not having the external air pressure to resist them
—and serious damage would be done to your body. Divers returning to the
surface too quickly from deep water often get the "bends," which arises from
these dissolved gases expanding into bubbles rather than escaping slowly from
the blood stream.
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Your Answer to Q35. Sorry, your answer is not correct. Think what happens to the wave on a rubber rope when it hits a wall.
Help: Fundamentals of Sound, Sec. 1-J.
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Hint for Question 35: When traveling waves of any kind hit a boundary, two things will happen: a portion of the wave energy will be reflected and a portion will be transmitted —just as in Question 25. Sound waves behave in a similar manner.
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Correct Answer to Question 35: When the sound wave in a canyon hits a hard wall most of the wave energy will be reflected back as an echo because the wall has so much inertia; little wave energy actually enters the rock. It helps to have a narrow canyon, because the wave energy is then channeled down the canyon rather than spreading out over a broad area and becoming less loud. Note that the hard wall is helpful to reflection; if a sound wave hits a soft material like a drapery a lot of wave energy is lost in the friction of the drape fibers and only a little is reflected. Thus one can make a quiet room by having a lot of carpeting, drapes, and soft furniture.
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Your Answer to Q40. Sorry, your answer is not correct. The information on the medium motion is irrelevant.
Help: Fundamentals of Sound, Sec. 1-C.
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Hint for Question 40: To get wave velocity you need distance traveled by the wave divided by time to travel that distance. Do not confuse the medium velocity and wave velocity.
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Correct Answer to Question 40: The 1/2 foot a rod goes up is the distance involved in the medium motion and is known as the amplitude. This and the time for it to happen are irrelevant to the problem. The distance traveled by the wave is 3 feet, which happens in 2 seconds. Thus the wave velocity is 3 feet/2 seconds = 3/2 ft/s.
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