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  • The frequency of echo will be____________ if the train blowing a whistle of frequency <img alt="320

The frequency of echo will be____________ \mathrm{Hz} if the train blowing a whistle of frequency 320 \mathrm{~Hz} is moving with a velocity of 36 \mathrm{~km} / \mathrm{h} towards a hill from which an echo is heard by the train driver. Velocity of sound in air is 330 \mathrm{~m} / \mathrm{s}.

Option: 1

340


Option: 2

-


Option: 3

-


Option: 4

-


Answers (1)

best_answer

\mathrm{f_{o}=320\: Hz}

Velocity of train \mathrm{=36\frac{km}{hr}}

                        \mathrm{=36\times \frac{5}{8}\frac{m}{s}}

                        \mathrm{=10{m}/{s}}

\mathrm{=f_{0}\left ( \frac{V}{V-V_{s}} \right )}

\mathrm{=320\times \left ( \frac{330}{330-10} \right )}

\mathrm{=330Hz}

Frequency of echo heard by train driver is

\mathrm{f_{2}=f_{1}\left ( \frac{V+V_{0}}{V} \right )}

    \mathrm{=330\left ( \frac{330+10}{330} \right )}

\mathrm{f_{2}=340Hz}

Posted by

rishi.raj

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