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標題:
doppler's effect??
發問:
You are standing on the road. When a car is moving towards you, you hear a frequency of 80Hz. When the car is moving away from you, you hear a frequency of 60Hz. What is the speed of the car? The speed of sound is 343 m/s.
Since it is the sound soure that is moving, use the Doppler Effect formula, the apparent frequency f is: f = (fo)[c/(c-v)] where fo is the original frequency of sound c is the speed of sound in air v is the speed of the sound source (+ve if moving towards the observor, and -ve if moving away from the oberveor) Hence, 80 = (fo)[343/(343-v)] and 60 = (fo)[343/(343+v)] Dividing, 80/60 = (343+v)/(343-v) i.e. v = 49 m/s
其他解答:
doppler's effect??
發問:
You are standing on the road. When a car is moving towards you, you hear a frequency of 80Hz. When the car is moving away from you, you hear a frequency of 60Hz. What is the speed of the car? The speed of sound is 343 m/s.
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最佳解答:Since it is the sound soure that is moving, use the Doppler Effect formula, the apparent frequency f is: f = (fo)[c/(c-v)] where fo is the original frequency of sound c is the speed of sound in air v is the speed of the sound source (+ve if moving towards the observor, and -ve if moving away from the oberveor) Hence, 80 = (fo)[343/(343-v)] and 60 = (fo)[343/(343+v)] Dividing, 80/60 = (343+v)/(343-v) i.e. v = 49 m/s
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