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Question
Solve the following problem.
A police car travels towards a stationary observer at a speed of 15 m/s. The siren on the car emits a sound of frequency 250 Hz. Calculate the recorded frequency. The speed of sound is 340 m/s.
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Solution
Given: vs = 15 m/s, n0 = 250 Hz, v = 340 m/s
To find: Frequency (n)
Formula: n = `"n"_0("v"/("v" - "v"_"s"))`
Calculation: As the source approaches listener, apparent frequency is given by,
n = `250 (340/(340 - 15)) = 3400/13`
∴ n = 261.54 Hz
The frequency heard by the audience as the car approaches stand is 261.54 Hz.
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