10. One of the loudest sounds in recent history was that made by the explosion o
ID: 1307040 • Letter: 1
Question
10. One of the loudest sounds in recent history was that made by the explosion of Krakatoa on August 26-27, 1883. According to barometric measurements, the sound had a decibel level of 180 dB at a distance of 161 km. Assuming the intensity falls off as the inverse of the distance squared, what was the decibel level on Rodriguez Island, 4800 km away?
dB
11. A sound wave from a siren has an intensity of 91.1 W/m2at a certain point, and a second sound wave from a nearby ambulance has an intensity level 9 dB greater than the siren's sound wave at the same point. What is the intensity level of the sound wave due to the ambulance?
dB
W/m2
13.The area of a typical eardrum is about 5.0 ? 10-5m2.
(a) Calculate the sound power (the energy per second) incident on an eardrum at the threshold of hearing.
W
(b) Calculate the sound power incident on an eardrum at the threshold of pain.
W
14. The toadfish makes use of resonance in a closed tube to produce very loud sounds. The tube is its swim bladder, used as an amplifier. The sound level of this creature has been measured as high as 98 dB.
(a) Calculate the intensity of the sound wave emitted.
W/m2
(b) What is the intensity level if six of these fish try to imitate six frogs by saying "Budweiser" at the same time?
dB
15. An outside loudspeaker (considered a small source) emits sound waves with a power output of 115 W.
(a) Find the intensity 9.5 m from the source.
W/m2
(b) Find the intensity level in decibels at that distance.
dB
(c) At what distance would you experience the sound at the threshold of pain, 120 dB?
m
16. Two trains on separate tracks move toward one another. Train 1 has a speed of 105 km/h, train 2 a speed of 55.0 km/h. Train 2 blows its horn, emitting a frequency of 500 Hz. What is the frequency heard by the engineer on train 1? (Assume the speed of sound is 345 m/s.)
Hz
17.At rest, a car's horn sounds at a frequency of 460 Hz. The horn is sounded while the car is moving down the street. A bicyclist moving in the same direction with one-third the car's speed hears a frequency of 418 Hz. What is the speed of the car? (Take the speed of sound in air to be 345 m/s.)
m/s
Is the cyclist ahead of or behind the car?
aheadbehind
18. An alert physics student stands beside the tracks as a train rolls slowly past. He notes that the frequency of the train whistle is 445 Hz when the train is approaching him and 441 Hz when the train is receding from him. Using these frequencies, he calculates the speed of the train. What value does he find?
m/s (Assume the speed of sound is 345 m/s.
)
Explanation / Answer
10)The intensity drops by a factor of (161/4800)^2 = 0.00112504
The decibel change = 10*log10(0.00112504) = -29.48 dB
Resulting dB is 180-29.48 = 150.52 dB.
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