Two cars are moving on two perpendicular road towards a crossing with uniform speeds of `72km//h` and `3km//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^@` angle with the roads, will be

Options

A. `321Hz`
B. `298Hz`
C. `289Hz`
D. `280Hz`

Answer

B

Explanation

Here `v_A=72(km)/(hr)=20(m)/(sec)`
`v_B=36km//hr=10m//sec`
`n=n((v+v_Bcos45^@)/(v-v_Acos45^@))`
`impliesn'=280((340+10//sqrt2)/(340-20//sqrt2))=298Hz`