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Homework Help: Light from Sun to Earth in seconds

  1. Feb 26, 2006 #1
    I'm a middle school student who enjoys astronomy and I volunteer at a local science center. At that science center I have no trouble answering questions about the visual aspect of astronomy, but I do run into some trouble when I am asked about the "techy" or mathmatical side of the science. Therefore, I went to the local used book store and picked up "Universe (fifth edition)" to enhance my knowledge of some of the mathmatical formulas used in astronomy. I'm having a bit of difficulty answering this question:

    The speed of light is 3.00 x 10^8 m/s. How long does it take light to travel from the Sun to Earth? Give your answer in seconds, using powers-of-ten notation.

    The answer is 4.99 x 10^2

    As far as I can tell, I have not overlooked anything in the chapter. Here is my work and my answer (1.496 x 10^8 being the distance from the earth to the sun in meters)

    Step 1- 1.496 x 10^11m = (3.00 x 10^8m/s)(t)

    Step 2- 1.496 x 10^11m / 3.00 x 10^8m/s= t

    Step 3- 499m/s x 10^3s = t

    Step 4- 4.99 x 10^5s = t

    Answer- 4.99 x 10^5s= t

    What am I doing wrong here?

    Forgive me if this thread is redundant, in the wrong forum, or too easy to for an answer :biggrin:

  2. jcsd
  3. Feb 26, 2006 #2


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    Staff Emeritus
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    1.496 / 3.00 is not 499.

    I think I know what you did:

    I bet you asked your calculator to compute:

    (1.496 x 10^11) / (3.00 x 10^8)

    to which it replied `499'.

    Then, you computed 10^11 / 10^8 = 10^3.

    And then said the answer was 499 x 10^3.

    But you already asked your calculator to deal with that part -- so it was wrong to do it again.
    Last edited: Feb 26, 2006
  4. Feb 26, 2006 #3
    O, sorry, I checked my work several times and thought I had cleared it of careless errors. Thanks!
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