wave_mechanics critical_thinking Question 13
Question: Two cars are moving on two perpendicular roads towards a crossing with uniform speeds of 72 km/hr and 36 km/hr. If first car blows horn of frequency 280 Hz, then the frequency of horn heard by the driver of second car when line joining the cars make 45° angle with the roads; will be
[RPET 1997]
Options:
A) 321 Hz
B) 298 Hz
C) 289 Hz
D) 280 Hz
Show Answer
Answer:
Correct Answer: B
Solution:
Here $ v _{A}=72km/hr=20m/\sec $
$ v _{B}=36km/hr=10m/\sec $
$ n’=n( \frac{v+v _{B}\cos 45^{o}}{v-v _{A}\cos 45^{o}} ) $
$ \Rightarrow $ $ n’=280( \frac{340+10/\sqrt{2}}{340-20/\sqrt{2}} )=298Hz $
BETA
