Two whistles $A$ and $B$ each have a frequency of $500\,Hz$. $A$ is stationary and $B$ is moving towards the right (away from $A$) at a speed of $50\,m/s$. An observer is between the two whistles moving towards the right with a speed of $25\,m/s$. The velocity of sound in air is $350\,m/s$. Assume there is no wind. Then which of the following statements are true:

  • A
    The apparent frequency of whistle $B$ as heard by $A$ is $444\,Hz$ approximately.
  • B
    The apparent frequency of whistle $B$ as heard by the observer is $469\,Hz$ approximately.
  • C
    The difference in the apparent frequencies of $A$ and $B$ as heard by the observer is $4.5\,Hz$.
  • D
    Both $(B)$ and $(C)$.

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What is the Doppler effect? Write its example and explain how its analysis can be performed.

When the observer moves towards a stationary source with velocity $V_{1}$,the apparent frequency of the emitted note is $F_{1}$. When the observer moves away from the source with velocity $V_{1}$,the apparent frequency is $F_{2}$. If $V$ is the velocity of sound in air and $F_{1} / F_{2} = 2$,then $V / V_{1}$ is equal to:

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