Question

The siren of a police car is heard by a sitting at a cafe. The police car is traveling at 1.10 x 105 km/hr. If the siren has a frequency of 1.02 kHz, calculate the frequency heard by the person as the car moves towards and then away from them.

Answer #1

(A) When the frequency heard by the person as car moves towards him

As we the doppler formula

f(L) = (c + v (L)) / ( c - v(S)) * f(S) ...........................(1)

Where f(L) = listener frequency, f(S) = source frequency , v(L) = listiner velocity . v(S) source velocity and c = speed of light (343 m/s)

Here person is at rest so

v(L) = 0 m/s

v(S) = 1.10 * 105 = 115.5 Km/hr

f(S) = 1.02 kHz or 1020 Hz

f(L) = ?

Putting these values in equation (1)

f(L) = ( 343 + 0)/(343-115.5) * 1020

**f(L) = 1537.8
Hz or 1.537 kHz**

(B) Now the frequency of siren when car move away from him

Now the formula is

f(L) = (c + v (L)) / ( c + v(S)) * f(S)

f(L) = ( 343 + 0)/(343 + 115.5) * 1020

**f(L) = 763 Hz
or 0763 kHz**

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Answer
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A.
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# tries: 1
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A police car is sounding a siren with 1340 Hz on a 20°C
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Answers must be within 2 Hz of correct answer.
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Save
Status
A.
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Hints: 0,0
# tries: 1
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