Question

A siren placed at a railway platform is emitting sound of frequency `5 kHz`. A passenger sitting in a moving train `A` records a frequency of `5.5kHz` while the train approaches the siren. During his return journey in a different train `B` he records a frequency of `6.0 kHz` while approaching the same siren. the ratio the velocity of train `B` to that of train `A` is
A. `242//252`
B. `2`
C. `5//6`
D. `11//16`

Answer 1

Correct Answer - B

In both the cases observer is moving towards the source. Hence by using `n=n((v+v_0)/(v))`
when passenger is sitting in train A, then
`5.5=5((v+v_A)/(v))` …(i)
When passenger is sitting in train B, then
`6=5((v+v_B)/(v))` ..(ii)
On solving equation (i) and (ii) we bet `(v_B)/(v_A)=2`.