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Concepts Of Physics MCQ Edition [Volume 1]PhysicsSound Waves

A person travelling in a car moving at 72 km/h blows a whistle that emits a wave of frequency 1250 Hz . Determine the frequency heard by another person standing on the road in front of the car. The speed of sound in air is 340 m/s .

Options

  1. A1328 Hz
  2. B1176 Hz
  3. C1250 Hz
  4. D1181 Hz

Correct answer

A. 1328 Hz

Step-by-step solution

Speed of the car (source), v_s = 72 km/h = 72 5 18 m/s = 20 m/s Speed of sound, v = 340 m/s Actual frequency of the whistle, f₀ = 1250 Hz Since the car is moving towards the stationary observer, the apparent frequency f is given by the Doppler effect formula: f = f₀ ( v v - v_s ) Substituting the given values: f = 1250 ( 340 340 - 20 ) f = 1250 ( 340 320 ) f = 1250 17 16 f = 1328.125 Hz The frequency heard by the person is approximately 1328 Hz .

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