Mathematical and Physical Journal
for High Schools
Issued by the MATFUND Foundation
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# Problem P. 4406. (January 2012)

P. 4406. A sound source is at rest and emits a sound of frequency f0=250 Hz for some time. The driver of the car which is moving towards the source at a speed of v, detect this sound the frequency of which is f'=263 Hz, and he hears the sound exactly as long as he covers a distance of s=82 m, along a straight line. a) What is the speed of the car? b) For how long did the sound source emit the sound?

(5 pont)

Deadline expired on February 10, 2012.

Sorry, the solution is available only in Hungarian. Google translation

Megoldás. $\displaystyle a)$ A jármű sebessége

$\displaystyle v=\frac{f'-f_{0}}{f_{0}}c_{\rm hang}\approx 64~\frac{\rm km}{\rm h }.$

$\displaystyle b)$ A hangforrás

$\displaystyle T=\frac{s}{v}\, \frac{f'}{f_{0}}\approx 4{,}9~\rm s$