A train moves towards a stationary observer with a speed $34 \,m / s$. The train sounds a whistle and its frequency registered by the observer is $f_1$. If the speed of the train is reduced to $17 \,m / s$, the frequency registered is $f_2$. If the speed of sound is $340 \,m / s$ then the ratio $\frac{f_1}{f_2}$ is ..........
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(d)
$f=f_0 \frac{v}{v-v_s}$
$f_1=f_0 \frac{340}{340-34}$
$f_2=f_0 \frac{340}{340-17}$
$f_1=\frac{10}{9} f_0$
$f_2=\frac{20}{19}$
$\frac{f_1}{f_2}=\frac{19}{18}$
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