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Velma and Mort relative motion question

  1. Oct 23, 2014 #1
    1. The problem statement, all variables and given/known data

    1. Velma passes Mort at a speed of 0.75c. At this speed, the "time dilation factor" is 1.5. In other words, Mort observes a 1-second tick of Velma's clock to take 1.5 seconds. Suppose that they are born at the same time, and that Mort observes himself to live 30 years. As Mort dies, how old will he observe Velma to be?
    A.) 45 years
    B.) 30 years
    C.) 20 years
    D.) 10 years
    E.) 40 years

    2. Suppose that you are inside a smooth-flying [no bumps] jet plane that is speeding up along a straight line. Can you detect this acceleration without directly or indirectly making use of anything outside of your own reference frame? If so, how could you observe this; and if not, why not?
    A.) No, because of the principle of relativity.
    B.) No, because of the principle of the constancy of lightspeed.
    C.) No, because jet planes move far too slowly for such an effect to actually be observed.
    D.) Yes. For example, if you dropped a coin you would find that it lands to the front of the drop point.
    E.) Yes. For example, if you dropped a coin you would find that it lands to the rear of the drop point.
    2. Relevant equations

    3. The attempt at a solution

    1. (C) -I'm not exactly sure why....
    2. (D) -Just makes sense to me....

    Thank you!
  2. jcsd
  3. Oct 23, 2014 #2


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    Gold Member

    1. C is correct. You should do the math so that you see exactly why. If you don't know how to do the math, figure it out. Don't guess.

    2. No, it's not D. The generally idea of your answer is right but how do you figure the coin would move FORWARD? Does your body tend to move forward as a jet takes off? Does it tend to move forward, away from the seat back, when you accelerate your car?

    EDIT: Oh, perhaps you are thinking of dropping a coin OFF of the plane. Then it WOULD land to the rear, but that's cheating. If you can look out the window, you KNOW you are accelerating. I don't think that's intended as part of the problem.
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