A car is travelling at a constant velocity directly towards a man standing in the middle of the road.The driver sounds the car’s horn as a warning. The horn emits a sound wave of constantfrequency.The frequency of the sound heard by the man is different from the frequency of the sound emittedby the horn.Which statement is correct?A The frequency of the sound emitted by the horn is greater than the frequency of the soundheard by the man.B The frequency of the sound heard by the man depends on the distance between the car andthe man.C The sound waves continually accelerate as they move from the horn to the man.D The wavelength of the sound heard by the man is less than the wavelength of the soundemitted by the horn.
Question
A car is travelling at a constant velocity directly towards a man standing in the middle of the road.The driver sounds the car’s horn as a warning. The horn emits a sound wave of constantfrequency.The frequency of the sound heard by the man is different from the frequency of the sound emittedby the horn.Which statement is correct?A The frequency of the sound emitted by the horn is greater than the frequency of the soundheard by the man.B The frequency of the sound heard by the man depends on the distance between the car andthe man.C The sound waves continually accelerate as they move from the horn to the man.D The wavelength of the sound heard by the man is less than the wavelength of the soundemitted by the horn.
Solution
The correct statement is D. The wavelength of the sound heard by the man is less than the wavelength of the sound emitted by the horn. This is due to the Doppler effect, which states that the frequency (and thus the wavelength) of a wave changes for an observer moving relative to the source of the wave. In this case, as the car is moving towards the man, the sound waves are compressed, resulting in a higher frequency and a shorter wavelength heard by the man compared to the sound emitted by the horn.
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