1.) A bat flies toward a wall at a speed of 4.5 m/s. As it flies, the bat emits
ID: 1303884 • Letter: 1
Question
1.) A bat flies toward a wall at a speed of 4.5 m/s. As it flies, the bat emits an ultrasonic sound wave with frequency 31.5 kHz. What frequency does the bat hear in the reflected wave?
______kHz
2.) A pipe that is open at both ends has a fundamental frequency of 326 Hz when the speed of sound in air is 343 m/s.
(a) What is the length of the pipe?
____ m
(b) What are the next two harmonics?
1st Harmonic = _____ Hz
2nd Harmonic = _____ Hz
3.) A physicist at a fireworks display times the lag between seeing an explosion and hearing its sound, and finds it to be 0.700 s.
(a) How far away is the explosion if air temperature is 22.0
Explanation / Answer
1) fwall = [ v / (v - vsource) ] f0
= [ 343 / (343 - 4.5) ] 31.5
= 31.92 KHz
fobs = [ (v + vobs) / v ] fwall
= [ (343 + 4.5) / 343 ] 31.92
= 32.34 KHz
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3) vw = 331 sqrt [T(k) / 273 ]
= 331 sqrt [295 / 273 ]
= 344.0
d = vw t = 344.0 * 0.700 s
= 240.8 m
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