Doppler Effect?
You are standing on a train station platform as a train goes by close to you. As the train approaches, you hear the whistle sound at a frequency of f1 = 92 Hz. As the train recedes, you hear the whistle sound at a frequency of f2 = 79 Hz. Take the speed of sound in air to be v = 340 m/s.
Find the numeric value, in hertz, for the frequency of the train whistle fs that you would hear if the train were not moving.
You are standing on a train station platform as a train goes by close to you. As the train approaches, you hear the whistle sound at a frequency of f1 = 92 Hz. As the train recedes, you hear the whistle sound at a frequency of f2 = 79 Hz. Take the speed of sound in air to be v = 340 m/s.
Find the numeric value, in hertz, for the frequency of the train whistle fs that you would hear if the train were not moving.
1 Answer
Explanation:
As an estimate I would expect the frequency to be about halfway between the two values i.e
We can show this as follows:
When the train is approaching we get:
Where v is the speed of sound.
We can find the speed of the train
When the train is receding we get:
Putting in the numbers we get:
Now divide
This is the speed of the train.
Now we can substitute this value back into
From the prediction this seems reasonable.