Sound & Doppler Effect — A/L Physics

How do I practise Sound & Doppler Effect?

1 question with a worked solution

1. A police siren emits sound of frequency 600 Hz. The police car moves towards a stationary pedestrian at a speed of 30 m s⁻¹. Taking the speed of sound in air as 330 m s⁻¹, what apparent frequency is heard by the pedestrian?
   1. A) 660 Hz
   2. B) 720 Hz
   3. C) 545 Hz
   4. D) 600 Hz
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   Correct answer: A) 660 Hz

   Using the Doppler effect formula for a moving source approaching a stationary observer: f' = f [v / (v - v_s)]. Here v = 330 m s⁻¹, v_s = 30 m s⁻¹, f = 600 Hz. Therefore, f' = 600 × [330 / (330 - 30)] = 600 × (330 / 300) = 600 × 1.1 = 660 Hz.

   Show worked solution

   Step 1: Doppler formula for approaching source: f' = f [v / (v - v_s)]. Step 2: Substitute: f' = 600 × [330 / (330 - 30)] = 600 × (330 / 300) = 660 Hz. Answer: 660 Hz.
   Modelled on: the A/L Physics examination pattern

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Where does Sound & Doppler Effect fit in the syllabus?

Unit 3.5 · Year 1 · Term 2