The whistle of an engine moving at `30km//h` is heard by a motorist driving at `15km//h` and he estimated the pitch to be 500. What would be the actual pitch if two are approaching each other ? Velocity of sound is 1220km//h .

Explanation

Here, `upsilon_(s)=30km//h, upsilon_(L)=15km//h, v^(')=500`
As the two are approaching each other,
`v^(')=((upsilon+upsilon_(L))v)/((upsilon-upsilon_(s)))`
`500=((1220+15)v)/(1220-30)=(1235v)/(1190)`
`:. v=(1190xx500)/(1235)=481.8Hz`