# The Doppler Effect

## Formulas Used

- Suppose that a 129 Hz buzzer is attached to a baseball that is thrown at 31.3 m/s. What frequency would a stationary person hear while waiting to catch the incoming ball? Use 342 m/s for the speed of sound.
- An emergency worker is driving at 32 m/s toward the source of a tornado alert siren. If she perceives the frequency of the siren to be 1110 Hz, what is the siren’s true frequency if the air temperature is 22 °C?
- A predatory bird is chasing its prey at 20.2 m/s when it emits a 282 Hz squawk. If the prey is moving away from the predator at 13 m/s, what frequency will it hear if the air temperature is 2.0 × 10
^{1}°C? - Two ambulances are approaching an accident scene from opposite directions. The ambulance coming from the north is traveling at 32 m/s and blaring a siren with a frequency of 1084 Hz. If the ambulance coming from the opposite direction is going 28 m/s, what frequency will its occupants hear from the first ambulance’s siren? Use 341 m/s for the speed of sound.
- A driver sitting at a railroad crossing perceives that the train’s whistle has a frequency of 157 Hz after it passes by. If the people on the train hear a frequency of 176 Hz, how fast is the train moving? Use 335 m/s for the speed of sound.
- How fast would one have to move toward a stationary tuning fork emitting a 348 Hz tone in order for it to sound as if the tone were only 328 Hz? Assume an air temperature of 26 °C.

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