A train moving at a speed of 220 ms-1 towards a stationary object emits a sound of frequency 1000 Hz. Some of the sound reaching the object gets reflected back to the train as echo. The frequency of the echo as detected by the driver of the train is:

(Speed of sound in air is 330 ms-1)

  • Option 1)

    4000 Hz

  • Option 2)

    5000 Hz

  • Option 3)

    3000 Hz

     

  • Option 4)

    3500 Hz

 

Answers (1)

As discussed in @9345

Frequency of the echo detected by the driver of the train:

V'=\left( \frac{v+u}{v- u} \right )V= \left( \frac{330+220}{330-220} \right )\times 1000=5000 Hz

 


Option 1)

4000 Hz

This option is incorrect.

Option 2)

5000 Hz

This option is correct.

Option 3)

3000 Hz

 

This option is incorrect.

Option 4)

3500 Hz

This option is incorrect.

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