A train coming toward you at 15 m/s blasts a signal which you hear as 400 Hz. What frequency will you hear after the train passes? Assume the speed of sound is 343 m/s.
Laura,I am not going to do your thinking for you. I will be happy to critique it.
Read your lesson about the Doppler effect and apply the appropriate formula.
I guess a better addition to the question would be which form of the equation would one use? Also, in the case of the source velocity, would it be (-) implying a velocity away from the observer or would it be (+) as a default? I have the same question on a practice exam.
To determine the frequency you will hear after the train passes, we need to consider the phenomenon of the Doppler Effect. The Doppler Effect describes how the perceived frequency of a wave changes when the source or the observer is in motion relative to each other.
In this case, the train is the source of the sound wave, and you are the observer. The train's motion causes a change in the frequency of the sound wave that you hear.
The formula for the observed frequency of a moving source is given by:
f' = (v + vo) / (v + vs) * f
- f' is the observed frequency (the frequency you will hear after the train passes)
- f is the emitted frequency (the frequency of the signal blast, which is 400 Hz)
- vo is the velocity of the observer (which is 0 since you are not in motion)
- vs is the velocity of the source (which is 15 m/s, the speed of the train)
- v is the speed of sound (which is 343 m/s)
Substituting the given values into the formula, we can calculate:
f' = (343 + 0) / (343 + 15) * 400
≈ 379 Hz
Therefore, the frequency you will hear after the train passes is approximately 379 Hz.