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Physics (AS & A Level) · Oct / Nov 2025 · Paper 12 · Question 27

9702Doppler effect for sound waves

A moving source emits sound of frequency 1200 Hz. A stationary observer hears sound of frequency 960 Hz. The speed of the sound is 340 m s⁻¹. What could be the velocity of the source?

  1. A68 m s⁻¹ directly away from the observer
  2. B68 m s⁻¹ directly towards the observer
  3. C85 m s⁻¹ directly away from the observer
  4. D85 m s⁻¹ directly towards the observer

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Correct answer: C. 85 m s⁻¹ directly away from the observer

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