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04192013  #1 
Join Date: Apr 2013
Posts: 1

Doppler Effect: Precalculus homework help???
The Doppler Effect (named after Christian Doppler) is the change in the pitch (frequency) of the sound from a source (s) as heard by an observer (o) when one or both are in motion. If we assume both the source and the observer are moving in the same direction, the relationship is: f' = fa(vvo/vvs)
where f' = perceived pitch by the observer fa = actual pitch of the source v = speed of sound in air (assume 772.4 mph) vo = speed of the observer vs = speed of the source Suppose you are traveling down the road at 45 mph and you hear an ambulance (with siren) coming toward you from the rear. The actual pitch of the siren is 600 hertz. a) Write a function f'(Vs) that describes this scenario. b) If f' = 620 Hz, find the speed of the ambulance. 
04202013  #2  
Join Date: Dec 2008
Posts: 249

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b) 620 = 600((772.4  45)/(772.4  vs)) (620/600) = (727.4/(772.4  vs)) 1.0333 = 727.4/(772.4  vs) 31/30 = 727.4/(772.4  vs) Cross multiplying gives: (30)(727.4) = (31)(772.4  vs) 21822 = 23944.4  31vs 31vs = 2122.4 vs = 68.465 mph 

04252013  #3  
Join Date: Oct 2012
Posts: 340

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