Question

A loudspeaker in a parked car is producing sound whose frequency is 20950 Hz. A healthy young person with normal hearing is standing nearby on the sidewalk but cannot hear the sound because the frequency is too high. When the car is moving away from the person, the person can hear the sound. If the speed of sound is 343 m/s, what is the minimum speed of the moving car?

Answer 1

359 m/s

Step-by-step explanation:

Highest frequency a person can hear is 20,000Hz.

f = c × λ

Frequency = Wave speed × Wavelength

Wavelength = 20,000 ÷ 343 = 58.31m

Wavespeed = Frequency ÷ Wavelength

c = 20,950 ÷ 58.31 = 359.3 m/s

= 359 m/s (3 s.f.)