A train's whistle emits a sound at a frequency of 450 hz and is moving at 30 m/s, what will be the perceived frequency of someone on the tracks if the speed of sound that day is 330 m/s?

Question

anonymous · Answer

since 30 is much smaller than 330 (and you're not told whether the person is in front of or behind the train) you can use the approximation
$$f = \Big(1+\frac{\Delta v}{c}\Big)f_0$$

anonymous · Answer

the person is in front of the train

anonymous · Answer

Do you know what dopppler shift is?!

anonymous · Answer

You should use the doppler sound formula, not the one above (for light). See: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/dopp.html

anonymous · Answer

what?

anonymous · Answer

can someone just plug in the various numbers and show me the equation with the numbers in it? i can do the math from there

anonymous · Answer

take a look at that web page. it explains exactly what you need to calculate your answer.

anonymous · Answer

we are here to help, not do! f is frequency. f (observed) means f (perceived). f (source) is the frequency emitted. v is speed of sound from the question. v (source) is the speed of the source. you should be able to put the numbers in there now..

anonymous · Answer

not asking you to do

anonymous · Answer

asking you to set it up :P

anonymous · Answer

Also - sorry @broken_symmetry your formula is fine, obviously just need to use the speed of the relevant waves (so v_sound not c here).

anonymous · Answer

sorry hitman, not going to set it up either. As a teacher there is no point in me providing you with basically the answer where you just have to calculate the numbers.

anonymous · Answer

He is right Hitman :P.. can you try setting up the equation? review ur notes maybe? :)

anonymous · Answer

I many texts, $c$ can stand for the propagation of any kind of wave in a medium. It's not restricted to the speed of light.