wave_mechanics dopplers_effect Question 27
Question: A motor car blowing a horn of frequency 124vib/sec moves with a velocity 72 km/hr towards a tall wall. The frequency of the reflected sound heard by the driver will be (velocity of sound in air is 330 m/s)
[MP PET 1997]
Options:
A) 109 vib/sec
B) 132 vib/sec
C) 140 vib/sec
D) 248 vib/sec
Show Answer
Answer:
Correct Answer: C
Solution:
Similar to previous question The frequency of reflected sound heard by the driver $ {n}’=n( \frac{v-(-v _{0})}{v-v _{s}} )=n( \frac{v+v _{0}}{v-v _{s}} ) $
$ =124[ \frac{330+(72\times 5/18)}{330-(72\times 5/18)} ] $ = 140 vibration/sec.
BETA
