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.

4.4 kHz

Explanation:

The frequency of the beats is given by the frequency of the original ultrasound, , and the frequency of the ultrasound reflected back from the car, :

(1)

The frequency of the reflected wave can be found by using the Doppler effect formula:

where

v = 340 m/s is the speed of sound

is the speed of the car

is the frequency of the original sound

Substituting,

So, the beat frequency (1) is

what is the question?

wavelegth as in spectrum red oygbiv