Finding velocity of a vehicle using Doppler Shift for sound

AI Thread Summary
The discussion revolves around calculating the velocity of a vehicle using the Doppler effect, with given frequencies of 1100 Hz and 950 Hz as the vehicle approaches and recedes. Participants express confusion about rearranging the formula to solve for the speed of the source, noting the presence of two unknowns. It is highlighted that the frequency should increase as the source approaches, necessitating a correct formulation of the equations. A suggestion is made to improve the clarity of the equations using LaTeX formatting. The conversation emphasizes the importance of accurately applying the Doppler effect principles to solve the problem.
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Homework Statement



You are standing on the side of the Trans-Canada Highway as the Physicsmobile approaches you. As it approaches, you hear an engine noise of 1100 Hz. After it passes, you hear an engine noise of 950 Hz. How fast was the Physicsmobile travelling?

Homework Equations



FMHlj.png

f2 = apparent frequency
f1 = actual frequency emitted by source
v = speed of sound in air
vs = speed of source

The Attempt at a Solution



I'm not sure how to re-arrange the formula. If I fill in all variables that I'm given, there are still two left blank (vs and f).
 
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You have two unknown values (vs and f1) and two equations - one before and one after it passes you. You can solve this equation system to get vs.
 
Does this look right?
 
nawg04 said:
Does this look right?

Your first equation is wrong. The source approaches the observer, so the frequency should increase. To increase the frequency, the denominator in the equation should decrease.
 

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