The Dropper EffectTiffany Yang

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Question 1:

•A police siren emits a frequency of 600.0 Hz. When the police car approaches you at a speed of 80.0km/h, what frequency do you perceive?

Solution

• The speed of the source, the policy car, is 80.0km/h=22.2m/s

• The speed of the receiver, you, is 0m/s

• The speed of the sound in air is 343m/s

• Emits frequency is 600.0Hz

• We can substitute all the information into the equation:

Calculation:

f=(343+0)/(343-22.2)*(600.0Hz)=641.52Hz

Does the solution makes sense?

The solution is reasonable because as the car approaches we hear a higher pitch.

Question 2:

• A police siren emits a frequency of 600.0 Hz. When the police car moves away from you at a speed of 80.0km/h, what frequency do you perceive?

SolutionWe have the exactly same information as the first question:

• The speed of the source, the policy car, is 80.0km/h=22.2m/s

• The speed of the receiver, you, is 0m/s

• The speed of the sound in air is 343m/s

• Emits frequency is 600.0Hz

Solution

• Therefore, we can use the same equation:

• However, we need to chose the bottom sign since the car is moving away from us.

Calculation:

f=(343-0)/(343+22.2)*(600.0Hz)=563.53Hz

Does the solution makes sense?

The solution is reasonable because as the car moves away we hear a lower pitch.