Physics: Apoliceman in a stationary car measures the speed of approaching cars by means of an ultrasonic device that emits a sound with a frequency of 41.2 khz. a car is approaching him at a speed of 33.0 m/s. the wave is reflected by the car and interferes with the emitted sound producing beats. what is the frequency of the beats? the speed of sound in air is 330 m/s.

His theory was that they revolved around the sun (heliocentric)....

Apoliceman in a stationary car measures the speed

landonp101

12.01.2022

4.6 kHz

Explanation:

The formula for the Doppler effect allows us to find the frequency of the reflected wave:

$f'=(\frac{v}{v-v_s})f$

where

f is the original frequency of the sound

v is the speed of sound

vs is the speed of the wave source

In this problem, we have

f = 41.2 kHz

v = 330 m/s

vs = 33.0 m/s

Therefore, if we substitute in the equation we find the frequency of the reflected wave:

$f'=(\frac{330 m/s}{330 m/s-33.0 m/s})(41.2 kHz)=45.8 kHz$

And the frequency of the beats is equal to the difference between the frequency of the reflected wave and the original frequency:

f_B = |f'-f|=|45.8 kHz-41.2 kHz|=4.6 kHz

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