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Homework Help: Question between friends! - How long to travel 1 light year?

  1. Sep 13, 2013 #1
    Question between friends! -- How long to travel 1 light year?

    1. The problem statement, all variables and given/known data

    Me and a few friends were trying to work out how long it would take a human to travel one light year. We were using the these variables.

    Distance = 9.4605284 × 1015 m

    Fastest speed for manned space travel = 39,846 kph or 11068.3 m/s

    2. Relevant equations

    I was using the equation of speed = distance/time, rearranged to solve for time. T = D/S

    3. The attempt at a solution

    My attempt brought me back the answer of 27084 years.

    I was doing this.

    9.46 x 1015 =854716299241 seconds or 27084 years
    11068 m/s

    If there is any other variables I have left out, could you please write back. Me and my friends have used different speeds, different units and our heads are now fried!!!

    Thank you
  2. jcsd
  3. Sep 13, 2013 #2


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    about 27,000 years looks good!
  4. Sep 13, 2013 #3


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    Did your friends get the same answer?If you are rounding the numbers,then you would get different answers.Your conversion of seconds to years is wrong!
  5. Sep 16, 2013 #4
    Your absolutely correct for the seconds to years conversion! Last time i'll ever use Google as a calculator!

    New answer is 27102.876054065195 or 27103 years.
  6. Sep 16, 2013 #5


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    Actually, Google's answer is fine. The length of the year is approximately 365.24 days.

    In any case, since you rounded off the distance to only three sig figs in the beginning, your final answer is only good to two or three sig figs as well. So answers like 27084 years or 27103 years are not really correct because the last two digits aren't significant.
  7. Sep 16, 2013 #6

    Andrew Mason

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    There are 365.25*24*3600 = 3.15576 x 107 seconds in a year.

    The speed of light is 2.99792458x108 m/sec

    So there are 2.99792458x108 x 3.15576 x 107 = 9.4607 x 1015 metres or 9.4607 x 1012 km in a light year.

    If the spaceship can travel 11.068 km/sec. then in 3.15576 x 107 seconds it can travel 3.8659 x 108 km.

    So it would take: 9.4607 x 1012 /3.8659 x 108 = 2.4472 x 104 = 24,472 years to make the journey.

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