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Homework Help: Proper Time earth to Pluto

  1. Nov 29, 2009 #1
    1. The problem statement, all variables and given/known data

    A spaceship leaves earth, travels to Pluto (which os 5 hours of distance away at the time), and then returns to earth in exactyly 11 hours later. assume the spaceships acceleration time is very short so it is always traveling at a constant speed. also assume that earth and pluto are approximately at rest to eachother and the sun during the journey.

    a- what is the speed of the ship during each part of the journey?
    b- calculate the time measured by the ships clock during the entire trip.

    2. Relevant equations
    speed= distance / time

    (1-v)^1/2 (change in t from a to b)= proper time

    3. The attempt at a solution

    I'm not sure what to do because i dont understand how the spaceshp can travel at a constant speed and take 5 hours to get there and 5 hours to get back. I am missing something.
  2. jcsd
  3. Nov 29, 2009 #2


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    Science Advisor
    Homework Helper

    Since you wrote sqrt(1-v^2) it looks like you are working in units where the speed of light c=1. Then to say Pluto is 5 hrs away really means that it's (5hrs)*c away or 5 hours travelling at the speed of light. When working in units where c=1, you are sort of allowed to be sloppy and drop factors of c.
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