Problem 12.61 A stationary police car emits a sound of frequency 1205 Hz that bo
ID: 1461936 • Letter: P
Question
Problem 12.61
A stationary police car emits a sound of frequency 1205 Hz that bounces off of a car on the highway and returns with a frequency of 1265 Hz . The police car is right next to the highway, so the moving car is traveling directly toward or away from it.
Part A
How fast was the moving car going?
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Part B
Was the moving car moving towards or away from the police car?
Please ChooseIt's was moving towards the police car. It's was moving away from the police car.
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Part C
What frequency would the police car have received if it had been traveling toward the other car at 16.0 m/s ?
Problem 12.61
A stationary police car emits a sound of frequency 1205 Hz that bounces off of a car on the highway and returns with a frequency of 1265 Hz . The police car is right next to the highway, so the moving car is traveling directly toward or away from it.
Part A
How fast was the moving car going?
v = m/sSubmitMy AnswersGive Up
Part B
Was the moving car moving towards or away from the police car?
Please ChooseIt's was moving towards the police car. It's was moving away from the police car.
SubmitMy AnswersGive Up
Part C
What frequency would the police car have received if it had been traveling toward the other car at 16.0 m/s ?
f = HzExplanation / Answer
Part A :
The police car hears the reflected sound from the car. So the car is the source and the police car is the observer. Since the apparent frequency increases, we can conclude that the car is moving towards the police car. Here, observer is stationary while source is moving towards the observer.
f' = f x v/(v-vs)
or, 1265 = 1205 x 340/(340-vs) (taking speed of sound in air, v = 340 m/s)
or, 340-vs = 1205 x 340/1265 = 323.87
or, vs = 16.13 m/s
So, the moving car is going at 16.13 m/s.
Part B :
It was moving towards the police car.
Part C :
f' = f x (v + v0)/(v - vs)
= 1205 x (340 + 16)/(340 - 16.13)
= 1205 x 356/323.87
= 1324.54 Hz.
So, the police car would have received a frequency of 1324.54 Hz.