91Ó°ÊÓ

What frequency is received by a mouse just before being dispatched by a hawk flying at it at \(25.0 \mathrm{m} / \mathrm{s}\) and emitting a screech of frequency \(3500 \mathrm{Hz} ?\) Take the speed of sound to be \(331 \mathrm{m} / \mathrm{s}.\)

A commuter train blows its 200-Hz horn as it approaches a crossing. The speed of sound is \(335 \mathrm{m} / \mathrm{s}\). (a) An observer waiting at the crossing receives a frequency of \(208 \mathrm{Hz}\). What is the speed of the train? (b) What frequency does the observer receive as the train moves away?

What beat frequencies result if a piano hammer hits three strings that emit frequencies of \(127.8,128.1,\) and \(128.3 \mathrm{Hz} ?\)

(a) What is the fundamental frequency of a 0.672 -m-long tube, open at both ends, on a day when the speed of sound is \(344 \mathrm{m} / \mathrm{s} ?\) (b) What is the frequency of its second harmonic?

If a wind instrument, such as a tuba, has a fundamental frequency of \(32.0 \mathrm{Hz}\), what are its first three overtones? It is closed at one end. (The overtones of a real tuba are more complex than this example, because it is a tapered tube.)

What length should an oboe have to produce a fundamental frequency of \(110 \mathrm{Hz}\) on a day when the speed of sound is \(343 \mathrm{m} / \mathrm{s} ?\) It is open at both ends.

Find the sound intensity level in decibels of \(2.00 \times 10^{-2} \mathrm{W} / \mathrm{m}^{2}\) ultrasound used in medical diagnostics.