Answer to Question #164378 in Optics for Cheryl-Ann

Question

 The driver of the stationary car can hear the frequency of the sound either directly from the alarm of the car or from a bridge ahead.

(a.) Name the phenomenon that permits the driver of the stationary car to hear the sound from the bridge.

 (b.) At what frequencies does the driver of the stationary car hear the sounds?

 (c.) The stationary car starts moving towards the bridge at a speed of 6ms~1. At what frequencies does the driver now hears the sounds? Explain why he hears beats and calculate the beat frequency

Answer 1

(a.) The phenomenon that permits the driver of the stationary car to hear the sound from the bridge is called echo.

(b.) The driver of the stationary car hears the sounds at frequencies between 20 Hz to 20 kHz.

(c.) When the stationary car starts moving towards the bridge at a speed of 6m/s, the driver hears the frequencies of

$$f_l=f_{l0}(1+v/c)=20(1+6/343)=20.3\text{ Hz},\\ f_u=f_{u0}(1+v/c)=20(1+6/343)=20.3\text{ kHz}.$$