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NEET2012PhysicsWaves and SoundActual

A train moving at a speed of 220 ~ms ⁻¹ towards a stationary object, emits a sound of frequency 1000 ~Hz . Some of the sound reaching the object gets reflected back to the train as echo. The frequency of the echo as detected by the driver of the train is (speed of sound in air is 330 ~ms ⁻¹ )

Options

  1. A3500 ~Hz
  2. B4000 ~Hz
  3. C5000 ~Hz
  4. D3000 ~Hz

Correct answer

C. 5000 ~Hz

Step-by-step solution

From Doppler's shift, we know for this case aligned n^ & =n ( v+v_s v-v_s ) & =1000 ( 330+220 330-220 ) & =1000 ( 550 110 )=5000 ~Hz aligned

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