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JEE Advanced2011PhysicsWaves and SoundActual

A police car with a siren of frequency 8 kHz is moving with uniform velocity 36 ~km / h towards a tall building which reflects the sound waves. The speed of sound in air is 320 ~m / s . The frequency of the siren heard by the car driver is

Options

  1. A8.50 kHz
  2. B8.25 kHz
  3. C7.75 kHz
  4. D7.50 kHz

Correct answer

A. 8.50 kHz

Step-by-step solution

Apparent frequency of sound heard by car driver (observer) reflected from the building will be aligned f^ & =f ( v+v₀ v-v_s ) & =8 ( 320+10 320-10 ) & =8.5 kHz aligned Correct option is (a). Analysis of Question (i) Question is simple. (ii) Driver will listen two sounds, direct and reflected. Direct sound will be of 8 kHz as driver has no relative motion with the car. But reflected sound is of increased frequency because driver and image of car both are approaching towards each other.

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