Wave Mechanics Question 681
Question: Two trains move towards each other with the same speed. The speed of sound is 340 m/s. If the height of the tone of the whistle of one of them heard on the other changes 9/8 times, then the speed of each train should be
Options:
A) 20 m/s
B) 2 m/s
C) 200 m/s
D) 2000 m/s
Show Answer
Answer:
Correct Answer: A
Solution:
[a] Here, $ v’=\frac{9}{8}v $ Source and observer are moving in opposite direction, therefore, apparent frequency $ v’=v\times \frac{(v+u)}{(v-u)}\Rightarrow \frac{9}{8},v=v\times \frac{340+u}{340-u} $
$ \Rightarrow ,u=\frac{340}{17}=20,m/\sec $
BETA
