The security alarm on a parked car goes off and produces a frequency of 813 Hz. The speed of sound is 343 m/s. As you drive toward this parked car, pass it, and drive away, you observe the frequency to change by 72.1 Hz. At what speed are you driving?

Question

Physics

Drew Hammond

24 September, 05:36

The security alarm on a parked car goes off and produces a frequency of 813 Hz. The speed of sound is 343 m/s. As you drive toward this parked car, pass it, and drive away, you observe the frequency to change by 72.1 Hz. At what speed are you driving?

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Answers (1)

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Rosemary Mccarthy · Answer 1

You are driving at Vo = 15.2 m/s = 54.72 km/h

Explanation:

Δf = 72.1 Hz

f = 813 Hz

v = 343 m/s

Δf = f * [ (v - (-vo) / v) - (v - (vo) / v) ]

clearing vo:

Vo = 15.2 m/s