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AP EAMCET2006PhysicsWaves and Sound

An observer is standing 500 ~m away from a vertical hill. Starting between the observer and the hill, a police van sounding a siren of frequency 1000 ~Hz moves towards the hill with a uniform speed. If the frequency of the sound heard directly from the siren is 970 ~Hz , the frequency of the sound heard after reflection from the hill (in Hz) is about, (velocity of sound =330 ~ms ⁻¹ ) :

Options

  1. A1042
  2. B1032
  3. C1022
  4. D1012

Correct answer

B. 1032

Step-by-step solution

Sound heard directly f₁=f_o ( v v+v_s ) 970=1000 ( 330 330+v_s ) or v_s=10.2 ~m / s The frequency of reflected sound is given by f₂=f_o ( v v-v_s )=1000 ( 330 330-10.2 )= 1000 330 319.8 1032 ~Hz

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