A loudspeaker in a parked car is producing sound whose frequency is 20 510 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, however, this person can hear the sound.
(a) Is the car moving toward or away from the person? Why?
(b) If the speed of sound is 343 m/s, what is the minimum speed of the moving car?