APPHY6.WSdoppler
Mr. Nestojko
March 17, 2015
1. A factory siren indicating the end of a shift has a frequency of 80 Hz where the speed
of sound in air is 343 m/s. What frequency is perceived by the occupant of a car that is
traveling at 20 m/s (a) towards the factory and (b) away from the factory?
2. As you stand by the side of the road ,a car approaches you at a constant speed,
sounding its horn, and you hear a frequency of 76 Hz. After the car goes by, you hear a
frequency of 65 Hz. The speed of sound in the air is 343 m/s.
a) What is the frequency of the sound emitted by the horn?
b)What is the speed of the car?
3. You are driving along a highway at 35.0 m/s when you hear the siren of a police car
approaching you from behind at constant speed and you perceive the frequency as 1340
Hz. You are relieved that he is in pursuit of a different driver when he continues past you,
but now you perceive the frequency as 1300 Hz. What is the speed of the police car? The
speed of sound in air is 343 m/s. What is the speed of the police car?
4. You are driving along a highway at 25.0 m/s when you hear the siren of an emergency
vehicle traveling at constant speed in the opposite direction on the other side of the
highway. When the vehicle is approaching you, you hear the frequency of the siren as
2380 Hz, but when it is past you the frequency becomes 1680 Hz. What is the frequency
of the siren? The speed of sound in air is 343 m/s.
5. A whistle produces sound of frequency of 1.00 kHz. If a listener moves with a speed
of 20 m/s away from the whistle, what frequency does this person hear if the sound speed
is 340 m/s?
6. You are moving at 120 km/h toward a stationary train. The train blows its 0.400-kHz
whistle. Take the speed of sound to be 340 m/s. What frequency do you hear?
7.You are moving at 120 km/h toward a stationary train. The train blows its 0.500-kHz
whistle. Take the speed of sound to be 340 m/s. What frequency do you hear?
8. What is the frequency heard by a person driving at 15 m/s toward a blowing factory
whistle (800. Hz) if the speed of sound is 341 m/s? What frequency would he hear after
passing the factory if he continues at the same speed?
9. A car approaching a stationary observer emits 450. Hz from its horn. If the observer
detects a frequency of 470. Hz, how fast is the car moving? The speed of sound is 343
m/s.
10. A burglar alarm is wailing with a frequency of 1200 Hz. What frequency does a cop
hear who is driving towards the alarm at a speed of 40.0 m/s? The air temperature is
35.0oC.
APPHY6.WSdoppler
Mr. Nestojko
March 17, 2015
challenge question:
Two identical cars are driving toward one another and sounding their horns. You’re the
driver of one of the cars. You measure your car’s horn to be sounding at 512 Hz, but you
measure the horn of the other car to be sounding at 600. Hz. The speed of sound is 345
m/s. If you are traveling at 26.8 m/s (60 mph), how fast is the other car traveling?