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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 points)

Deadline expired on 10 February 2012.

Google Translation (Sorry, the solution is published in Hungarian only.)

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

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