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Doppler Shift Quiz Answers

  1. While waiting for your bus you hear in the distance the familiar drone of its engine. After a short while the tone begins to sound lower and lower. Knowing about it's Doppler shift, what should you do?
    Pick up your back-pack and get ready, because the bus will soon stop for you.
    Run because the bus is accelerating uncontrollably toward you.
    Walk home because the bus has already passed you and is accelerating toward the school.
    Start walking toward the spot where the school bus is stopped.
    None of the Above.

  2. Your youngest sibling is amazingly able to produce a long steady whine for hours on end. While trying to hide from her, you hear the pitch of the iritable noise increase and then decrease. What has just happened?
    Your sibling ran away from you. (A)
    Your sibling ran past you. (B)
    You are amazed at how fast your sibling can run since you are able to notice the Doppler shift in her voice. (C)
    A and C.
    B and C.

  3. While driving your car, you are stopped for running a red light. You tell the police officer that because of the Doppler shift, the red light (650 nm) was blueshifted to a green light (470 nm) as you drove towards the stop light. How fast would you have to be going in order for this to be true?
    0.5 times the speed of light
    0.3 times the speed of light
    0.1 times the speed of light
    0.01 times the speed of light
    70 mph

    4. Note! In this case, in order to be correct, you would have to use the relativistic Doppler shift equation to find the exact answer. The non-relativistic equation only applies in the low-velocity limit (less than 0.1 times the speed of light). You can see that you'd have to be going pretty fast to use this excuse for running a red light!

Return Click here to return to solving for M31's velocity by examining its spectrum.

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