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  • Help me understand! - Oscillations and Waves - JEE Main-5

Two cars are moving in 2 perpendicular roads towards a crossing with speeds of 72 km/hr and 36km/hr. If first car blows horn of 280 Hz then frequency of horn heard by driver of second car when line joining the car makes 45\degree C with roads, will be

  • Option 1)

    321 Hz

  • Option 2)

    298 Hz

  • Option 3)

    289 Hz

  • Option 4)

    280 Hz

 

Answers (1)

best_answer

n' = n\left [ \frac{v + v_{b} \cos 45\degree}{v-v_{a}\cos 45\degree} \right ]

n' = 280\left [ \frac{340 + 101\sqrt{2}}{340-20\sqrt{2}} \right ]= 298 Hz

 

Doppler Effect when source and observer are not in line -

\nu _{ap}= \nu _{0}\left [ \frac{V+V_{2}\cos \Theta _{2}}{V-V_{1}\cos \Theta _{1}} \right ]

 

 

- wherein

V_{1}\: and \: V_{2} are velocities of car 1 and car 2 respectively 

\Theta _{1}\: and \: \Theta _{2} are angle shown in the fig.

 

 


Option 1)

321 Hz

This is incorrect

Option 2)

298 Hz

This is correct

Option 3)

289 Hz

This is incorrect

Option 4)

280 Hz

This is incorrect

Posted by

Aadil

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