A car is parked 23.0 m directly south of a railroad crossing. A train is approac

Question

A car is parked 23.0 m directly south of a railroad crossing. A train is approaching the crossing from the west, heading directly east at a speed of 57.0 m/s. The train sounds a short blast of its 305-Hz horn when it reaches a point 20.0 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

Hypotenuse H^2 = 20^2 + 23^2

H = 30.47 m

Cos theta = 23/30.47 = 0.754

so frequency f = (c/(C -V cos theta)) * V

f = 305 * ( 343 )/(343- 57* 0.754)

f = 348.7 Hz

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