Solve Doppler Problems: Train & Person

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In summary, the train's speed and the frequency of the whistle can be used to calculate the frequency that the person will hear as the train approaches and recedes. The formula to use is f = fi*V/(V + Vs), where V is the speed of sound in air and Vs is the speed of the source. Since the receiver is not moving, Vs must be made negative to account for the train's movement towards the person.
  • #1
cyspope
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Homework Statement


A train approaches an observer at 35.0 m/s and passes a person stading on the side of the track. The whistile is sounding at 2.5 kHz. What frequency will the person hear as the train approaches? When it recedes?

Homework Equations


f' = f [tex]\frac{v \pm vo}{v \mp vs}[/tex]

The Attempt at a Solution


f' = 2500 Hz(?)

I don't know what number I should put into the equation.
 
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  • #2
Yes, what a miserable formula that is!
It looks a little better here: http://en.wikipedia.org/wiki/Dopplar_Effect
(scroll down 1 screenfull)
Since the receiver is not moving, the formula is
f = fi*V/(V + Vs)
Here V is the speed of sound in air, and Vs is the speed of the source. The speed of the source toward the receiver increases the frequency, so you must make Vs a negative number (dividing by a smaller number makes the result larger).
 
  • #3


I would suggest that the person use the given information to determine the velocity of the train relative to the observer, as well as the velocity of sound in air. This can then be used to calculate the observed frequency using the equation provided. It is important to note that the observer's velocity (vo) should be negative when the train is approaching and positive when it is receding. Additionally, the direction of the train's velocity (vs) should be consistent with the direction of the observer's velocity. By plugging in the appropriate values, the person should be able to calculate the observed frequency for both scenarios.
 

FAQ: Solve Doppler Problems: Train & Person

1. How does the Doppler effect affect the sound of a train passing by a person?

The Doppler effect causes a change in the frequency of sound waves as the source of the sound moves closer or further away from the observer. In the case of a train passing by a person, the frequency of the sound waves will increase as the train approaches the person and decrease as the train moves away from the person.

2. What factors influence the Doppler effect in a train and person scenario?

The factors that influence the Doppler effect in this scenario include the speed of the train, the distance between the train and the person, and the frequency of the sound waves emitted by the train. The speed of the train and the distance between the train and the person will determine the rate at which the frequency of the sound waves changes.

3. How can the Doppler effect be used to determine the speed of a train?

By measuring the change in frequency of the sound waves as the train passes by a stationary observer, the speed of the train can be calculated using the formula v = (f/f0 - 1)c, where v is the speed of the train, f is the observed frequency, f0 is the original frequency, and c is the speed of sound.

4. Can the Doppler effect be observed with other types of waves besides sound?

Yes, the Doppler effect can also be observed with other types of waves such as light waves. This is known as the optical Doppler effect and is commonly observed in astronomy when measuring the speed of stars and galaxies.

5. How does the Doppler effect play a role in the development of technology, such as radar and sonar?

The Doppler effect is used in technology such as radar and sonar to measure the speed and distance of objects by analyzing the change in frequency of the waves that are reflected off of them. This allows for the detection of moving objects, such as airplanes or submarines, and is crucial in various industries such as aviation and marine navigation.

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