Physics (AS & A Level) · May / June 2021 · Paper 13 · Question 25

A train's whistle is emitting sound of frequency 500 Hz as the train moves with a speed of 20 m s⁻¹ along a straight track. The train moves directly towards a stationary observer standing next to the track and then passes the observer. The speed of sound in air is 330 m s⁻¹. What is the difference between the frequencies of the sound heard by the observer before and after the train has passed the observer?

1. A29 Hz
2. B32 Hz
3. C40 Hz
4. D61 Hz

As printed in the paper