 Doppler Effect: Precalculus homework help??? - XP Math - Forums Sign Up FREE! | Sign In | Classroom Setup | Common Core Alignment  XP Math - Forums Doppler Effect: Precalculus homework help??? 04-19-2013 #1 Denise44   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(v-vo/v-vs) 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.  04-20-2013   #2
MAS1   Join Date: Dec 2008
Posts: 249 Quote:
 Originally Posted by Denise44 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(v-vo/v-vs) 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.
a) f'(vs) = 600((772.4 - 45)/(772.4 - vs))

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  04-25-2013   #3    Join Date: Oct 2012
Posts: 340 Quote:
 Originally Posted by mas1 a) f'(vs) = 600((772.4 - 45)/(772.4 - vs)) 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
ooohhhhh
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