Physics (AS & A Level) · May / June 2025 · Paper 11 · Question 24

An aircraft produces a sound at a frequency of 30.0 Hz. The speed of sound in air is 330 m s$^{-1}$. The aircraft is directly in front of the stationary observer and travels in a straight line towards or away from the observer. The observer hears the sound from the aircraft at a frequency of 20.0 Hz. What is the speed and direction of the aircraft?

1. A110, away from observer
2. B110, towards observer
3. C165, away from observer
4. D165, towards observer

As printed in the paper