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  • A car P travelling at sounds its horn at a frequency of <img alt="400 \

A car P travelling at 20 \mathrm{~ms}^{-1} sounds its horn at a frequency of 400 \mathrm{~Hz}.Another car \mathrm{Q}  is travelling behind the first car in the same direction with a velocity 40 \mathrm{~ms}^{-1}.The frequency heard by the passenger of the car \mathrm{Q} is approximately [Take, velocity of sound =360 \mathrm{~ms}^{-1} ]

Option: 1

471 \mathrm{~Hz}


Option: 2

514 \mathrm{~Hz}


Option: 3

421 \mathrm{~Hz}


Option: 4

485 \mathrm{~Hz}


Answers (1)

best_answer

\mathrm{V}_{\mathrm{c}}=20 \mathrm{~ms}^{-1}
\mathrm{f}=400 \mathrm{~Hz}
\mathrm{Q} \rightarrow=40 \mathrm{~ms}^{-1} \quad \mathrm{P} \rightarrow 20 \mathrm{~ms}^{-1}
0\longleftarrow \mathrm{S}
\mathrm{f}_{\mathrm{app}}=\left[\frac{\mathrm{Vs}-\left(-\mathrm{V}_{\mathrm{Q}}\right)}{\mathrm{V}_{\mathrm{S}}-\left(-\mathrm{V}_{\mathrm{p}}\right)}\right] \mathrm{f}

=\left(\frac{360+40}{360+20}\right) \times 400=\frac{400}{380} \times 400=421 \mathrm{~Hz}   

Posted by

SANGALDEEP SINGH

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