A car is moving towards a huge wall with a sspeed c/10, where c = speed of sound in still air. A wind is also blowing parallel to the velocity of the car in the same direction and with the same speed. If the car sounds a horn of frequency f, then the frequency of the reflected sound of the horn heared by driver of the car is 9xf. Find the value of x :
Answers
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Answer:
x = 11/81
Explanation:
Formula to be used for Doppler's effect :
where f' is the frequency after modification.
v is the velocity of sound wave
is the velocity of observer
is the velocity of source
and, f is the actual frequency.
Solving everything with respect to car. So, the velocity of source initially will be zero. Velocity of observer (wall) will be c/10 towards car.
First case is when the sound of horn reaches the wall:
f' =
because, the source's (car's) speed is c/10.
and the observer's (wall) speed is 0.
f' =
f' =
In the second case also with respect to car, velocity of source (wall) is c/10 towards car. Velocity of observer (car) is zero.
Second case is when the sound of horn is reflected by the wall:
f' =
f' =
f' =
Given - f' = 9xf
so, 9xf = 11f/9
x = 11/81.
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