TUTORIAL ANSWERS 620-640

 
 
 

Your Answer to Q620.  Sorry, your answer is not correct.

Help: Fundamentals of Sound, Sec. 12-B.

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You should try to work out the answer on your own, but, if you insist on reading it, the correct answer is here.

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Hint for Question 620:  The small force applied to the long arm can lift the large force on the short arm.

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Your Answer to Q620. Congratulations, your answer is correct.

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Correct Answer to Question 620: The lengths of the arms are proportional the the weights. The heavy weight is 10 times the small force and so the long arm (at 1 m) must be 10 times the length of the short arm, which is then 1/10 m. b) is correct.

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Your Answer to Q625.  Sorry, your answer is not correct. 

Help: Fundamentals of Sound, Sec. 12-B.

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You should try to work out the answer on your own, but if you insist on reading it the correct answer is here.

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Hint for Question 625: The amplification factor tells one by how much she can enhance the force or pressure applied.  

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Your Answer to Q625. Congratulations, your answer is correct.

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Correct Answer to Question 625: The 5 N force has been amplified by the lever into a 50 N force. The amplification factor is 10. b) is the correct answer.

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Correct Answer to Question 630:  A megaphone is a cone shaped device whose opening at one end is approximately the size of the open mouth. It gradually widens to a much larger diameter, sometimes more than a foot across. In speaking, sound is reflected at the lips because of the discontinuity between the air tube of the vocal tract and the outside world. By having a cone that gradually opens to the outside air, the impedance difference between the vocal tract and the open air occurs gradually over the whole length of the megaphone rather than suddenly at the lips. Because there is no sudden impedance difference anywhere, less reflection occurs and more of the sound gets out of the vocal tract into open air. A louder sound results to the hearer.

The megaphone also concentrates the sound somewhat by directing it over a somewhat reduced area, but that is likely a smaller effect.

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Your Answer to Q635.  Sorry, your answer is not correct.

Help: Fundamentals of Sound, Sec. 12-K.

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You should try to work out the answer on your own, but if you insist on reading it the correct answer it is here.

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Hint for Question 635: Pressure is force divided by area. What area is relevant here?

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Your Answer to Q600. Congratulations, your answer is correct.

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Correct Answer to Question 635:  Pressure is force divided by area. If there are M nails, each nail provides a force of (700/M) Newtons to support the body, on an area of 2x10-7 m2. The pressure, when there is a minimal number of nails, is then 5x106 N/m2 = 700/(Mx2x10-7) N/m2 . Solve for M to get M = 700/(2x10-7x5x106) = 700. e) is the answer.

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Your Answer to Q640.  Sorry, your answer is not correct.

Help: Fundamentals of Sound, Sec. 11-K.

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Hint for Question 640:  Does the basilar membrane work this way?
 
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Your Answer to Q640. Congratulations, your answer is correct.

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Correct Answer to Question 640:  b) is correct. The description given fits the volley theory (which is sometimes called the "telephone theory") of hearing. For most frequencies our hearing is described by a place theory, so that a particular position on the basilar membrane is associated with a particular frequency. The diaphram in the old phone speaker has no particular position associated with any frequency; the whole thing vibrates at each frequency. Waves travel along the basilar membrane to the resonant position, so the traveling wave theory is equivalent to a place theory. At very low frequencies the whole basilar membrane is vibrating as a unit; at these frequencies there may be an analogy with the telephone diaphram.


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