Question

(PHYSICS HELP!) Two cars have identical horns, each emitting a frequency of fs = 409 Hz. One of the cars is moving with a speed of......?

Two cars have identical horns, each emitting a frequency of fs = 409 Hz. One of the cars is moving with a speed of 11.0 m/s toward a bystander waiting at a corner, and the other car is parked. The speed of sound is 343 m/s. What is the beat frequency heard by the bystander?

Answer 1

Given,

`f' = 409"Hz"`

`nu_"source" = (11.0"m")/"s"`

`nu_"snd" = (343"m")/"s"`

Recall, for a sound moving toward a stationary observer,

`f' = f/(1-nu_"source"/nu_"sound")`

Hence, the "real" frequency of the sound is,

`=> f = f'(1-nu_"source"/nu_"sound") approx 396"Hz"`

The beat frequency is merely the quantitative measure of the waves' interference in time. To be sure, it is the difference between frequencies.

By extension the beat frequency heard is,

`f_"B" = f' - f approx 13.1"Hz"`