Two train travelling in opposite directions at 126 km/hr each, cross other while one of them is whistling if the frequency of the node is 2.22 kHz find the apparent frequency as head by an observer in the other train :
(a) Before the trains cross each other
(b) After the trains have crossed each other `(V_("sound") = 335 m//sec)`

Explanation

Here `V_(1) = 126 xx (5)/(18) = 35 m//s`
(i) In this situation `rarr v_(1) v_(1) larr`
Observed frequency `n'=((v+v_(1))/(v-v_(1)))xxn=((335+35)/(335-35))xx2220=2738Hz`
(ii) In this situation `v_(1) larr rarr v_(1)`
Observed frequency `n'=((v-v_(1))/(v+v_(1)))xxn=((335-35)/(335+35))xx2220=1800Hz`