An aeroplane is flying at a height of 500 m. It sends a sound wave to the ground at 60 degree angle. Find the speed of the aeroplane if it is supposed to receive the echo? Take speed of sound 340 m/s
Answers
Answer:
Explanation:
Key Idea the perceived frequency heard by the observer depends upon the relative motion between observer and source.
If the source and observer are approaching each other, then the velocity of the source v
s
is positive and velocity of the listener v
l
is negative, the perceived frequency will be higher than the original.
Perceived frequency is given by
n
′
=n(
v−v
0
v+v
0
) [∵n
′
=n
v−v
s
v−(−v
0
]
Here, v=340m/s,v
0
=20m/s,
v
s
=20m/s,n=240Hz
Hence, n
′
=240(
340−20
340+20
)
=240×
320
360
=270Hz
Note When the speed of source and observer are much lesser than that of sound, the change in frequency becomes independent of the fact whether the source is moving or the observer.