Calculating Speed: Solving a Physics Wave Question | Homework Help

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SUMMARY

The problem involves a cyclist and a car approaching each other, with the car emitting a sound at 500 Hz and the cyclist perceiving it at 535 Hz. The correct approach to solve this involves using the general Doppler effect formula: f' = f(V + Vr) / (V - Vs), where both the source and receiver are in motion. The calculated speed of both the cyclist and the car is 11.6 m/s, confirming the expected result. This demonstrates the importance of applying the correct Doppler effect formula when both the source and receiver are moving.

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Homework Statement


a cyclist and a car are approaching each other at the same speed. the car makes a 500 Hz sound at 343 m/s. the cyclist hears the sound as 535 Hz. How fast are they moving?


Homework Equations



f2 = f1(v/v\pmvs)

The Attempt at a Solution


535 hz = 500 hz(343 m/s\div343 m/s-vs)
vs = 22.4 m/s

but the answer should be 11 m/s
HELP ??
 
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In this case, both the source and the receiver move, so u must use the general Dopple formula, not the specific formula for each case the source moves or the receiver moves.

f' = f.(V+Vr)/(V-Vs)

f': frequency received

f: frequency created.

V: speed of the wave (sound or light).

Vr: velocity of the receiver: positive if moving toward the source, otherwise it's negative.

Vs: velocity of the source: positive if moving toward the receiver, otherwise it's negative.

In this case, Vs=Vr, and they're both positive. U will get the result 11,6 m/s. Be happy :D
 
great thanks!
 

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