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# 'Doppler effect'

A truck is moving at 50 m/sec while its horn emits a steady note at 280 cy/sec.
A woman is stationary, 150 meters ahead of the truck.
A man is in a car, 200 meters ahead of the truck, moving toward the truck at a speed of 30 m/sec. The speed of the sound is 345 m/sec.
PART a. Find the frequency heard by the woman.
PART b. Find the frequency heard by the man in the car.
PART c. Find the wavelength of the sound ahead of the moving truck.
PART d. Find the period of the sound heard by the man.

#### Solution Preview

The 'Doppler effect' refers to the change in frequency of a sound when either the source or the observer, or both, are moving relative to one another. This change occurs because the wavelength of a sound from a movng source is different from that of a stationary source. If 'L' is the wavelengh of the sound from a stationary source, then the wavelength of from a moving source is 'less than L' ahead of, and 'more than L' behind a moving source.
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<br>The basic equation for the doppler effect is:
<br>(1) f' = f (v + vs)/(v - vo) in which:
<br>f is the frequency emitted by the source,
<br>f' is the requency received by the observer,
<br>v is the speed of the ...

#### Solution Summary

Doppler effect is applied

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