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Two cars, one in front of the other, are travelling down the highway at 25 m/s. The car behind sounds its horn, which has a frequency of 640 Hz. What is the frequency heard by the driver of the lead car? (Vsound=340 m/s).

The answer choices are:

A) 463 Hz
B) 640 Hz
C)579 Hz
D) 425 Hz
E) 500 Hz

Respuesta :

Answer:

[tex] f_s = 640 Hz[/tex]

Explanation:

For this case we know that the speed of the sound is given by:

[tex] V_s = 340 m/s[/tex]

And we have the following info provided:

[tex] v_c = 25 m/s [/tex] represent the car leading

[tex] v_s= 25 m/s[/tex] represent the car behind with the source

[tex] f_o = 640 Hz[/tex] is the frequency for the observer

And we can find the frequency of the source [tex] f_s[/tex] with the following formula:

[tex] f_s = \frac{v-v_o}{v-v_s} f_o [/tex]

And replacing we got:

[tex] f_s = \frac{340-25}{340-25} *640 Hz = 640 Hz[/tex]

So then the frequency for the source would be the same since the both objects are travelling at the same speed.

[tex] f_s = 640 Hz[/tex]

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