wave_mechanics dopplers_effect Question 44
Question: A train moves towards a stationary observer with speed 34 m/s. The train sounds a whistle and its frequency registered by the observer is $ f _{1} $ . If the train’s speed is reduced to 17 m/s, the frequency registered is $ f _{2} $ . If the speed of sound is 340 m/s then the ratio $ f _{1}/f _{2} $ is
[IIT-JEE (Screening) 2000]
Options:
A) 18/19
B) 1/2
C) 2
D) 19/18
Show Answer
Answer:
Correct Answer: D
Solution:
By using $ n’=n( \frac{v}{v-v _{S}} ) $
Therefore $ f _{1}=n( \frac{v}{v-v _{S}} ) $
$ =n( \frac{340}{340-34} )=\frac{340}{306}n $ and $ f _{2}=n( \frac{340}{340-17} )=n( \frac{340}{323} ) $
$ \Rightarrow $ $ \frac{f _{1}}{f _{2}}=\frac{323}{306}=\frac{19}{18} $
BETA
