Calculating Frequency of Train Whistle for Approaching Passenger

In summary, the frequency of the whistle of a train approaching a passenger on another train moving at a speed of 18.0 m/s and in the opposite direction is 228.46 Hz. This is calculated using the formula fapproach = (v-vL)/(v+vs) * fs, taking into account the relative motion of the source and observer. However, there may be a sign error in the calculation as the observed frequency should be higher, not lower.
  • #1
merlos
14
0
A train is traveling at 30.0 m/s relative to the ground in still air. The frequency of the note emitted by the train whistle is 262 Hz.
a. What frequency (fapproach) is heard by a passenger on a train moving at a speed of 18.0 m/s relative to the ground in a direction opposite to the first train and approaching it?



a. fapproach = (v-vL)/(v+vs) * fs



f= [(345m/s-18m/s)/(345m/s+30m/s)]*(262 Hz)
= 228.46 Hz

Wrong
 
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  • #2
Well, yeah! The frequency of the whistle of a train approaching you is higher, not lower. You have a sign error.
 
  • #3
merlos said:
A train is traveling at 30.0 m/s relative to the ground in still air. The frequency of the note emitted by the train whistle is 262 Hz.
a. What frequency (fapproach) is heard by a passenger on a train moving at a speed of 18.0 m/s relative to the ground in a direction opposite to the first train and approaching it?
a. fapproach = (v-vL)/(v+vs) * fs
f= [(345m/s-18m/s)/(345m/s+30m/s)]*(262 Hz)
= 228.46 Hz

Wrong


Careful. There are two sets of relative motion here. The source relative to the air and the observer relative to the air. You need to do a doppler calculation for each. As Halls pointed out, the observed frequency should be higher.

AM
 
  • #4
i don't get it///
 

FAQ: Calculating Frequency of Train Whistle for Approaching Passenger

What is the Doppler Effect on a train?

The Doppler Effect on a train is the perceived change in frequency of sound or light waves due to the relative motion between the train and an observer. This means that the frequency of the waves will appear to be higher as the train approaches the observer and lower as it moves away.

How does the speed of the train affect the Doppler Effect?

The speed of the train directly affects the Doppler Effect. As the train moves faster, the difference in frequency between the approaching and receding waves becomes greater, resulting in a more noticeable change in pitch.

Can the Doppler Effect be observed with any type of wave?

Yes, the Doppler Effect can be observed with any type of wave, including sound waves and light waves. However, the effect is most commonly associated with sound waves.

What is the formula for calculating the Doppler Effect on a train?

The formula for calculating the Doppler Effect on a train is: f' = f(v ± vr) / (v ± vs), where f' is the perceived frequency, f is the actual frequency, v is the speed of the wave, vr is the speed of the receiver (observer), and vs is the speed of the source (train).

How does the direction of the train affect the Doppler Effect?

The direction of the train does not affect the Doppler Effect. The perceived change in frequency will be the same regardless of whether the train is moving towards or away from the observer.

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