PH30S
WORKSHEET
Oak Park
WORKSHEET
Topic: Doppler Effect
Let the speed of sound be 340 m/s for all of the following problems unless otherwise stated.
1. A train approaching a station at a speed of 40 m/s sounds a 2000 Hz whistle.
a. What is the apparent frequency of the sound heard by an observer standing at
the station?
b. What is the frequency heard as the train passes the observer and is moving
away?
2. You are standing by the railroad track when a train sounding a 750 Hz whistle
approaches then passes you at 80 Km/h. What is the difference in frequencies you hear
as the train approaches and departs?
3. Two trains emit whistles of the same frequency, 380 Hz. If one train is at rest and the
other is moving away from the observer at 90 Km/h, what will the observer detect as
the beat frequency? (observer is stationary)
4. With what speed should a plane fly toward a stationary listener so that the apparent
frequency of a 1000 Hz sound is 1500 Hz?
5. What is the drop in frequency of the sound a listener hears as a train with a
320 Hz horn passes at 145 km/h?
6. A siren emits a sound at 1700 Hz. Assume a speed of sound of 332 m/s for this
question. What frequency is heard by a stationary observer if the car with the siren is
traveling at
a. 25 m/s toward the observer?
b. 25 m/s away from the observer?
c. 140 km/h toward the observer?
7. How fast and in what direction is a car moving if its horn frequency of 900 Hz is heard
by a stationary observer at 875 Hz?
8. Two people hear the 1700 Hz siren of an ambulance. One person is in front and the
other is behind the ambulance. If the ambulance is traveling at 120 km/h, what is the
difference in frequencies heard by the two people? Assume the speed of sound to be
333 m/s.
9. As a racing car zooms past you, its pitch decreases by 20%. How fast is the car
traveling?
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