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Chapter 12: Q1MCQ (page 328)
Do you expect an echo to return to you more quickly on a hot day or a cold day?
(a) Hot day.
(b) Cold day.
(c) Same on both days.
The correct option is (a).
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Traditional methods of protecting the hearing of people who work in areas with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new technology, headphones are worn that do not block the ambient noise. Instead, a device is used which detects the noise, inverts it electronically, then feeds it to the headphones in addition to the ambient noise. How could adding more noise reduce the sound levels reaching the ears?
You look directly overhead and see a plane exactly 1.45 km above the ground flying faster than the speed of sound. By the time you hear the sonic boom, the plane has traveled a horizontal distance of 2.0 km. See Fig. 12-38. Determine (a) the angle of the shock cone, \(\theta \), and (b) the speed of the plane and its Mach number. Assume the speed of sound is 330 m/s.
A fireworks shell explodes 100 m above the ground, creating colorful sparks. How much greater is the sound level of the explosion for a person at a point directly below the explosion than for a person a horizontal distance of 200 m away (Fig. 12-34)?
(III) A police car sounding a siren with a frequency of 1580 Hz is traveling at 120.0 km/h. (a) What frequencies does an observer standing next to the road hear as the car approaches and as it recedes? (b) What frequencies are heard in a car traveling at 90.0 km/h in the opposite direction before and after passing the police car? (c) The police car passes a car traveling in the same direction at 80.0 km/h. What two frequencies are heard in this car?
Question: (III) When a player鈥檚 finger presses a guitar string down onto a fret, the length of the vibrating portion of the string is shortened, thereby increasing the string鈥檚 fundamental frequency (see Fig. 12鈥�36). The string鈥檚 tension and mass per unit length remain unchanged. If the unfingered length of the string is l= 75.0 cm, determine the positions x of the first six frets, if each fret raises the pitch of the fundamental by one musical note compared to the neighboring fret. On the equally tempered chromatic scale, the ratio of frequencies of neighboring notes is 21/12.
Figure 12-36
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