An ambulance is traveling East at 20m/s. The siren emits a fixed frequency of 33

Question

An ambulance is traveling East at 20m/s. The siren emits a fixed frequency of 330Hz. Each of the following cars is traveling down the road as described. Determine if the driver of the car will hear a frequency the same as 330Hz, higher than 330Hz, or lower than 330Hz. I really suggest drawing a picture to help sort this out. HigherA car sitting stationary at the side of the road watching the oncoming ambulance. | Higher A car driving East at a speed of 20m/s. The car is in front of the ambulance. 1 Lower 1 A car driving west at a speed of 15m/s. The car has already passed the ambulance. | Same t A car driving East at a speed of 25m/s. The car is behind the ambulance

Explanation / Answer

frequency heard is given as

f' = (V - VL) f/(V - Vs)

for case 1 :

VL = velocity of listener = 0

Vs = velocity of sound source = 20

V = speed of sound = 343

so f' = (V - 0) f/(V - Vs) = 343 (330)/(343 - 20) = 350.4 Hz

case 2 :

VL = velocity of listener = 20

Vs = velocity of sound source = 20

V = speed of sound = 343

so f' = (V - 20) f/(V - Vs) = (343 - 20) (330)/(343 - 20) = 330 Hz

Case 3 :

VL = velocity of listener = - 15

Vs = velocity of sound source = 20

V = speed of sound = 343

so f' = (V - VL) f/(V - Vs) = (343 - (-15)) (330)/(343 - 20) = 365.8 Hz

case 4 :

VL = velocity of listener = 25

Vs = velocity of sound source = 20

V = speed of sound = 343

so f' = (V - VL) f/(V - Vs) = (343 - (25)) (330)/(343 - 20) = 325 Hz

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