Physics (AS & A Level) · Oct / Nov 2020 · Paper 12 · Question 25

An emergency vehicle sounds its siren as it accelerates along a straight road between two points X and Y, as shown in the diagram. 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?

1. 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
2. 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
3. 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
4. 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

As printed in the paper