Final answer:
The question pertains to the Doppler effect, which requires calculating the altered frequency heard by an observer moving relative to the source. The frequency heard by the passenger in the car will be slightly lower than the emitted frequency of 400 Hz, as from the car's perspective, the ambulance with a faster speed is moving away.
Step-by-step explanation:
Doppler Effect and Frequency Change
The question deals with the Doppler effect, which describes the change in frequency of a wave in relation to an observer who is moving relative to the wave source. In this case, an ambulance with a siren at 400 Hz is moving at 100 km/h while a car moves in the same direction at 80 km/h. To determine the frequency heard by the passenger in the car, we need to use the Doppler effect formula for sound waves:
f' = f (v + vo) / (v + vs)
Where:
- f' is the observed frequency
- f is the source frequency (400 Hz)
- v is the speed of sound in air (about 343 m/s under standard conditions)
- vo is the speed of the observer (car's speed converted to m/s)
- vs is the speed of the source (ambulance's speed converted to m/s)
Both the car and ambulance are moving in the same direction, but since the ambulance is faster, from the car's frame of reference, it would appear as if the source of the sound (ambulance) is moving away. Therefore, the observer in the car will hear a slightly lower frequency than 400 Hz due to the Doppler effect.