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Homework Help: Time Dialation Help

  1. Mar 31, 2008 #1
    [SOLVED] Time Dialation Help

    1. The problem statement, all variables and given/known data
    A bomb is placed on a space probe just before it's launched. The timer is set to trigger the bomb after exactly 24hrs. The probe travels away from Earth on a straight line at v=.9c. How long after launch will the observers on the Earth see the flash of light from the exploding bomb?

    2. Relevant equations

    [tex]\Delta\tau=\Delta t \sqrt{1-\frac{v^{2}}{c^{2}}}[/tex]

    3. The attempt at a solution
    [tex] \Delta\tau = 24hrs.[/tex]

    [tex]\Delta t = \frac{24hrs}{\sqrt{1-.9^{2}}} = 55hrs[/tex]
    But, the text book gives a time of 105hrs. Can anyone please tell me why what I did is wrong? This seems like a straightforward problem and I have no clue where I mesed up. Any help is greatly appreciated.
  2. jcsd
  3. Mar 31, 2008 #2
    You're half way,
    I think you need to add time for the light from the explosion to get back to earth - which is when people on earth see the explosion
    Calc how far away it is.
    Then calc the time for light to travel that distance.
  4. Mar 31, 2008 #3
    [tex]\Delta x = .9c(55hrs)[/tex]
    [tex]t = \frac{.9c(55hrs)}{c} = 49.5 hrs [/tex]

    Thank you for the help, I completely blanked that part!
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