A-LevelPhysicsWaves9702/12 · Oct/Nov 2020 · Q251 Mark
An emergency vehicle sounds its siren as it accelerates along a straight road between two points X and Y, as shown in the diagram. [Figure 25.1] The frequency of the sound emitted by the siren is 750 Hz. A person stands at X and another person stands at Y. What describes the sounds heard by the people at X and at Y as the vehicle accelerates?
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Asound heard by person at X: higher than 750 Hz, increasing in frequency; sound heard by person at Y: lower than 750 Hz, decreasing in frequency
Bsound heard by person at X: higher than 750 Hz, decreasing in frequency; sound heard by person at Y: lower than 750 Hz, increasing in frequency
Csound heard by person at X: lower than 750 Hz, decreasing in frequency; sound heard by person at Y: higher than 750 Hz, increasing in frequency
Dsound heard by person at X: lower than 750 Hz, increasing in frequency; sound heard by person at Y: higher than 750 Hz, decreasing in frequency
✓ Correct answer
C: sound heard by person at X: lower than 750 Hz, decreasing in frequency; sound heard by person at Y: higher than 750 Hz, increasing in frequency
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