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MHT CET202616 April 2026Evening ShiftPhysicsWaves and SoundActual

A person observes two moving trains. 'A' reaching the station and 'B' leaving the station with equal speed of 30m/s. If both trains emit sounds with frequency 300 Hz, (speed of sound = 330 m/s) difference of frequencies heard by the person will be

Options

  1. A10 Hz
  2. B33 Hz
  3. C55 Hz
  4. D80 Hz

Correct answer

C. 55 Hz

Step-by-step solution

Given: Speed of sound, v = 330 m/s Speed of trains, v_s = 30 m/s Actual frequency, f₀ = 300 Hz Apparent frequency of train A (moving towards the observer): f_A = f₀ ( v v - v_s ) f_A = 300 ( 330 330 - 30 ) = 300 ( 330 300 ) = 330 Hz Apparent frequency of train B (moving away from the observer): f_B = f₀ ( v v + v_s ) f_B = 300 ( 330 330 + 30 ) = 300 ( 330 360 ) = 275 Hz Difference in frequencies heard by the person: f = f_A - f_B = 330 - 275 = 55 Hz Answer: 55 Hz

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