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Light travels at 3.00 x 10^8 m/s. If the starlight from the Unicorn galaxy takes 1 year 47 days and 2 hours to reach us. How far away is it in kilometers?

  • chemistry -

    1 year=365 days

    365 + 47=412 days total

    412 days*(24hours/1 day)= 9,888 hours

    9,888 hours + 2 hours=9,890 hours total

    9,890 hours total*(60 min/1 hour)*(60 sec/1 min)= total time in seconds

    3.00 x 10^8 m/s*total time in seconds= distance in meters

    distance in meters*(1 kilometer/1,000m)= distance in kilometers

  • chemistry -

    9,890 hours total*(60 min/1 hour)*(60 sec/1 min)= total time in seconds

    is 35,604, 000 right?

  • chemistry-aira -

    Yes, 35,604,000 seconds, but what do you do with it once you have found the time that it takes in seconds?

  • chemistry -

    I multiply 35,604,000 by 3.00 x 10^8 to find out the distance in meters?

    which gives me 1.06812e+16??

    is that right?

  • chemistry -

    You will get an answer that is very large, so you will have to use scientific notation. Report no more then 3 significant figures.

  • chemistry -

    Yes, but only three significant figures. So, a number, decimal followed by two more numbers.

  • chemistry -

    so it will look like this :

    distance in meters (1.06)*(1 kilometer/1,000m) = distance in kilometers

    -> 0.00106 is the final answer?

  • chemistry -

    No, 1.06812e+16 is correct. But you are only suppose to report three significant figures: 1.07 e+16

  • chemistry -

    yeah, but I'm very confused on how to get the final answer. Do i take 1.07e+16 and multiply it by a thousand to get km?

  • chemistry -

    No. 1.07 x 10^16 is in meters; you have to take the whole thing and divide it by 1,000, not just 1.07.

    So, 1.07 x 10^16 m*(1km/1,000m)= your answer in Km

    ****Notice how the m's cancel and you are only left with km.

    The FINAL ANSWER SHOUD BE 1.07 x 10^13

  • chemistry -


    So, you have to make this relationship a fraction.


    But how do I organize it in a way that meters goes away and kilometers remain?


    So if I multiply the ration this way, by my intermediate answer that is in meters, then the meters cross cancel and you are only left with meters.

    I hope this makes more since.

  • chemistry -

    I GOT IT. thank you so much !! best tutor out here

  • chemistry -

    You are too nice. At least you can understand my typos. When I help others on another forum, I can edit my answers, so I do not look like an idiot, but on this forum I can not.

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