**Problem**

A police siren emits a frequency of 640 Hz. When the police car approaches you at a speed of 25 m/s, what frequency do you perceive when:

**1)** you are not moving

**2)** you are moving towards the police car at 5 m/s

**3)** you are moving away from the police car at 5 m/s.

Assume the speed of sound is 343 m/s.

**Solution**

Use the doppler shift formula

where is the shifted frequency, is the frequency of the source, is the speed of sound, is the speed of the receiver, and is the speed of the source.

**Part 1**

**Part 2**

**Part 3**

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