QJEEAdv07Ph0360: JEE Advanced 2007 Physics - Class 11 JEEAdv07Ph0360 Solution: The spread of frequency as observed by the passengers in train…

Frequency $(f') = {f_1}\left( {{{v - {v_0}} \over {v - {v_s}}}} \right) = 800\left[ {{{340 - 30} \over {340 - 20}}} \right]$

$=800 \times \frac{31}{32}$ ..... (i)

where, $\left(\frac{v-v_{0}}{v-v_{\mathrm{S}}}\right)=\frac{31}{32}$ ..... (ii)

Frequency $\left(f^{\prime}\right)=f_{2}\left(\frac{v-v_{0}}{v-v_{\mathrm{S}}}\right)=1120 \times \frac{31}{32}$ ..... (iii)

$\therefore \quad f^{\prime}-f^{\prime}=(1120-800) \frac{31}{32}=320 \times \frac{31}{32}$

$=310 \mathrm{~Hz}$