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Two engines pass each other moving in opposite directions with uniform speed of 30 m/s. One of them is blowing a whistle of frequency 540 Hz.  Calculate the frequency heard by driver of second engine before they pass each other.  Speed of sound is 330 m/sec :

  • Option 1)

     450 Hz

  • Option 2)

    540 Hz

  • Option 3)

     648 Hz

  • Option 4)

    270 Hz



Answers (1)


As we learnt in

Frequency of sound when source and observer are moving towards each other -

\nu {}'= \nu _{0}.\frac{C+V_{0}}{C-V_{\Delta }}

- wherein

C= Speed of sound

V_{0}= Speed of observer

V_{\Delta }= speed of source

\nu _{0 }= Original frequency

\nu {}'= apparent frequency


 \upsilon'=\left(\frac{330+30}{330-30} \right )\times540

\upsilon'=648\ Hz

Correct option is 3.


Option 1)

 450 Hz

This is an incorrect option.

Option 2)

540 Hz

This is an incorrect option.

Option 3)

 648 Hz

This is the correct option.

Option 4)

270 Hz


This is an incorrect option.

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