The frequency of a whistle is $300\text{ Hz}$. It is approaching towards an observer with a speed one-third…

The frequency of a whistle is $300\text{ Hz}$. It is approaching towards an observer with a speed one-third of the speed of sound. The frequency of sound as heard by the observer will be
  1. $450\text{ Hz}$
  2. $300\text{ Hz}$
  3. $400\text{ Hz}$
  4. $425\text{ Hz}$

Solution

Frequency of sound heard by observer, $f = 300 \left(\frac{v}{v - v/3}\right) = 450\text{ Hz}$

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