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JEE Main20204 Sep 2020Evening ShiftPhysicsWaves and SoundActual

The driver of bus approaching a big wall notices that the frequency of his bus's horn changes from 420 Hz to 490 Hz when he hears it after it gets reflected from the wall. Find the speed of the bus if speed of the sound is 330 ms – 1 :

Options

  1. A91   kmh - 1
  2. B81   kmh - 1
  3. C61   kmh - 1
  4. D71   kmh - 1

Correct answer

A. 91   kmh - 1

Step-by-step solution

Frequency appeared at wall f w = 330 330-v .f     . ..... (1) f ' = 330 + v 330 · f w = 330 + v 330 - v f 490 = 330 + v 330 - v · 420 v = 330 × 7 91 ≈ 25 . 38 m / s = 91 Km / s

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