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COMEDK2023PhysicsWaves and Sound

A car is moving towards a high cliff. The car driver sounds a horn of frequency f . The reflected sound heard by the driver has a frequency 2 f . If v be the velocity of sound, then the velocity of the car in the same velocity units, will be

Options

  1. Av 2
  2. Bv 3
  3. Cv 4
  4. Dv 2

Correct answer

B. v 3

Step-by-step solution

When the sound is reflected from the cliff, it approaches the driver of the car. Therefore, the driver acts as an observer and both the source (car) and observer are moving. Hence, apparent frequency heard by the observer (driver) is given by where, v_s= velocity of sound and v_o= velocity of the car Thus, Eq. (i) becomes aligned 2 f & =f ( v+v_o v-v_o ) 2 v-2 v_o & =v+v_o 3 v_o=v v_o= v 3 aligned

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