Understanding Doppler Shifts I

Classical Mechanics Level 3

Do you remember learning about Doppler Shifts?

When a fire engine sounds off its horn the pitch changes depending on whether it is coming towards you or away from you.

Suppose that you are standing near the sidewalk when a fire engine passes you by.

The fire engine is moving at a constant velocity for a long time.

I) You start to hear the fire engine at t = 0, when the fire engine is far away.

II) At t = 120s the fire engine is closest to you.

III) At t > 240s the fire engine is far away again.

Which of the following is true about the pitch from t = 0 to t > 240s?

Starting from t=0, the pitch decreases at first until t = 120s and then increases.. The pitch decreases monotonically from t=0 to t>240s. Starting from t=0, the pitch increases at first until t = 120s and then decreases. The pitch increases monotonically from t = 0 to t > 240s.

Max Yuen by Max Yuen , 42, USA

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1 solution

Paul Hansen
Jun 11, 2019

Think about what you have heard standing by the road...

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