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 5.5 kHz 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 of the velocity of train B to that of train A is

• A. 242/252
• B. 2
• C. 5/6
• D. 11/6

Answer 1

The correct option is B

2

In both the cases observer is moving towards, the source. Hence by using $n^{\prime }$ = $n\left(\frac{v+v_0}{v}\right)$

When passenger is sitting in train A, then

$5.5$ = $5\left(\frac{v+v_A}{v}\right)$ ......(i)

When passenger is sitting in train B, then

$6$ = $5\left(\frac{v+v_B}{v}\right)$

On solving equation (i) and (ii), we get $\frac{v_B}{v_A}$ = $2$