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Homework Help: Decay question

  1. Oct 7, 2005 #1
    for this question:
    a certain particle has a lifetime of 1*10^8 sec when measured at rest. How far does it go before decaying if its speed is 0.99c when it is created?

    my problem:
    because the particle is decaying, then its speed should be changing...
    then there's two variables in this problem!
    any suggestions?
     
  2. jcsd
  3. Oct 7, 2005 #2

    Physics Monkey

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    The particle doesn't change its speed until it decays, why would it? This is a standard time dilation problem I think.
     
    Last edited: Oct 7, 2005
  4. Oct 7, 2005 #3

    Astronuc

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    This is not correct. The decay is essentially instantaneous.

    One must think of the relativistic effects on time and distance - time dilation and length contraction.

    http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/tdil.html
     
  5. Oct 7, 2005 #4

    Doc Al

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    Don't worry about its speed after decaying. According to lab frame observers, what's the lifetime of the particle? (Hint: Time dilation.)
     
  6. Oct 7, 2005 #5

    Physics Monkey

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    Well we jumped all over this one. Haha.
     
  7. Oct 7, 2005 #6

    Doc Al

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    At least we're all saying the same thing. That's good. :smile:
     
  8. Oct 7, 2005 #7
    opps! lol...
     
  9. Aug 30, 2009 #8
    I thought I'd piggy back on this post since I have essentially the same question.

    A particle has a lifetime of 1.0E-7s when measured at rest. What distance does it travel if it is created at 0.99c?

    I use the time dilation equation to find t'. I get 1.41E-8s. I then multiply this by 0.99c and get 4.19m. The book says 210m.

    edit:
    Got it

    My book's wording gets the best of me, when it says 'at rest' it means the observer, not the particle itself.
     
    Last edited: Aug 30, 2009
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