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  • Two cars are moving on two perpendicular roads towards a crossing with uniform speeds of 72 km/h and 36 km/h. If first car blows horn of frequency 280 Hz,then the  frequency of horn heard

Two cars are moving on two perpendicular roads towards a crossing with uniform speeds of 72 km/h and 36 km/h. If first car blows horn of frequency 280 Hz,then the  frequency of horn heard by the driver of second car when line joining the cars make 45^{\circ} angle with the roads, will be 

Option: 1

321 Hz


Option: 2

298 Hz 


Option: 3

289 Hz


Option: 4

280 Hz


Answers (1)

best_answer

Here, \mathrm{V_A=72 \mathrm{~km} / \mathrm{h}=10 \mathrm{~m} / \mathrm{s} .}

\mathrm{\begin{aligned} & V_B=38 \mathrm{~km} / \mathrm{h}=10 \mathrm{~m} / \mathrm{s} . \\ & n^{\prime}=n\left(\frac{V+V_B \cos 45^{\circ}}{V-V_A \cos 45^{\circ}}\right) \end{aligned}.}

\mathrm{n^{\prime}=280\left(\frac{340+10 / \sqrt{2}}{340-20 / \sqrt{2}}\right)=298 \mathrm{~Hz}}

Posted by

Ritika Kankaria

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