A car is parked 21.0 m directly south of a railroad crossing. A train is approac

Question

A car is parked 21.0 m directly south of a railroad crossing. A train is approaching the crossing from the west, heading directly east at a speed of 56.0 m/s. The train sounds a short blast of its 320-Hz horn when it reaches a point 22.0 m west of the crossing. What frequency does the car's driver hear when the horn blast reaches the car? The speed of sound in air is 343 m/s. (Hint: Assume that only the component of the train's velocity that is directed towards the car affects the frequency heard by the driver.)

Explanation / Answer

tan theta = 21/22 angle of sound wave from track theta = 43.7 deg 56 * cos 43.7 = 40.5 m/s component of train speed towards car f = f0 * V / (V - 40.5) Doppler effect for moving source and stationary observer f = 320 * 343 / (343 - 40.5) = 363 / sec

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