Wave Mechanics Question 684
Question: A sound source emits frequency of 180 Hz when moving towards a rigid wall with speed 5 m/s and an observer is moving away from wall with speed 5 m/s. Both source and observer moves on a straight line which is perpendicular to the wall. The number of beats per second heard by the observer will be
[Speed of sound = 355 m/s]
Options:
A) 5 beats/s
B) 10 beats/s
C) 6 beats/s
D) 8 beats/s
Show Answer
Answer:
Correct Answer: A
Solution:
[a] Frequency heard by observer directly coming from source $ =\frac{355-5}{355+5}\times 180=175 $
$ Hz.,f _{2}\to $ frequency heard by observer after reflection $ =[ \frac{355}{355-5}\times ][ \frac{355-5}{355} ]\times 180=180Hz $
$ f _{2}-f _{1}=5,Hz $
BETA
