Question

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?

Answer 1

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

Step-by-step 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