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JEE Main201912 Apr 2019Evening ShiftPhysicsWaves and SoundActual

Two sources of sound S 1 and S 2 produce sound waves of same frequency 660 H z . A listener is moving from source S 1 towards S 2 with a constant speed u 0 m / s and he hears 10 b e a t s / s . The velocity of sound is 330 m / s . Then, u 0 equals:

Options

  1. A10.0 m / s
  2. B2.5 m / s
  3. C5.5 m / s
  4. D15.0 m / s

Correct answer

B. 2.5 m / s

Step-by-step solution

Frequency observed from S 1 :           f 1 = 660 330 - u 0 330 - 0 Frequency observed from S 2 :           f 2 = 660 330 + u 0 330 - 0 As f 2 - f 1 = 10 660 330 + u 0 330 - 0 - 330 - u 0 330 - 0 = 10 2 2 u 0 = 10 u 0 = 2.5   m / s

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