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Doppler Effect

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I am a little bit stuck on this question about the Doppler effect. It says A police car is traveling at 17m/s and has a siren emitting a sound at a constant 475hz. The speed of sound is 340m/s. Make a sketch of the frequency vs the time heard by an observer at the side. Label the f axis with actual values of min, max and middle frequencies. 

I understand the equations needed for the Doppler Effect but I don't understand how the frequency one involves time. Any help would be good:(

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As police car comes towards the observer, the apparent frequency is higher than the actual frequency but as it leaves the observer the apparent frequency is lower. 

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3 minutes ago, kw0573 said:

As police car comes towards the observer, the apparent frequency is higher than the actual frequency but as it leaves the observer the apparent frequency is lower. 

Thank you, but how would I add actual values to this? 

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They should have said how far away the police was initially from the observer, so you can calculate when it is directly where the observer is. Before the police car comes to the observer, the apparent frequency is one value, then afterwards it's another value. 

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57 minutes ago, kw0573 said:

They should have said how far away the police was initially from the observer, so you can calculate when it is directly where the observer is. Before the police car comes to the observer, the apparent frequency is one value, then afterwards it's another value. 

 

They haven't :( Thankyouuuu for your help though :)

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Just now, LuckyHoof said:

They haven't :( Thankyouuuu for your help though :)

In that case you only need to label the frequency axis but not the time axis

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