The Doppler Effect Homework: Speed of Train from 940Hz to 915Hz

In summary, the question is asking for the speed of a train passing a stationary observer on a platform, given the frequency of a flute note before and after passing the observer. The equation used is (Fs/Fo) - 1 * V, where Fs is the frequency heard by the observer, Fo is the frequency of the flute, and V is the speed of the train. The given options for the speed of the train are 7.3 m/s, 12 m/s, 21 m/s, 32 m/s, and 42 m/s. However, the correct answer is not among these options and the arithmetic may be incorrect or there may be missing information.
  • #1
san512
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0

Homework Statement


A train moving at a constant speed is passing a stationary observer on a platform. A flute player is playing a note with a frequency of 940Hz. after the flute has passed, the observer hears the sound frequency of 915Hz. What is the speed of the train? The speed of sound in air is 343m/s.

Homework Equations



Fo = Fs (1/(1+(Vs/V))

The Attempt at a Solution



Vs = ((Fs/Fo) - 1) * V

When i input the given information I keep getting the wrong answer. Is my arithmetic wrong or am I missing something completely?
 
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  • #2
What is the given answer and what are you getting?
 
  • #3
A) 7.3 m/s
B) 12 m/s
C) 21 m/s
D) 32 m/s
E) 42 m/s

I get 9.4 m/s
 
  • #4
Same here unfortunately.
 
  • #5


Your equations and approach seem correct. It is possible that there is a mistake in your arithmetic or that you are using incorrect values for the speed of sound or the frequencies. I would recommend double checking your calculations and making sure you are using the correct values for all variables. If you are still getting the wrong answer, it may be helpful to show your work and calculations to a teacher or tutor for assistance.
 

1. What is the Doppler Effect?

The Doppler Effect is a phenomenon in which the perceived frequency of a wave changes when the source of the wave is in motion relative to the observer. This effect is commonly observed with sound waves, but it can also occur with other types of waves, such as light waves.

2. How does the Doppler Effect impact the speed of a train?

The Doppler Effect can be used to calculate the speed of a train by comparing the frequency of the train's sound waves as it approaches and passes an observer. As the train approaches, the sound waves are compressed, resulting in a higher frequency. As the train moves away, the sound waves are stretched, resulting in a lower frequency. By measuring the difference in frequency, the speed of the train can be determined.

3. What is the formula for calculating the speed of a train using the Doppler Effect?

The formula for calculating the speed of a train using the Doppler Effect is: v = (f2 - f1) / (f2 + f1) * c, where v is the speed of the train, f1 is the initial frequency, f2 is the final frequency, and c is the speed of sound.

4. Can the Doppler Effect be used to measure the speed of any moving object?

Yes, the Doppler Effect can be used to measure the speed of any moving object, as long as the source of the wave is in motion relative to the observer. This can include objects such as cars, planes, and even stars.

5. How accurate is the calculation of speed using the Doppler Effect?

The accuracy of the calculation of speed using the Doppler Effect depends on several factors, such as the accuracy of the initial and final frequency measurements, the speed of sound, and any external factors that may affect the waves. However, with precise measurements and proper calculations, the Doppler Effect can provide a fairly accurate estimation of an object's speed.

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