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Time = distance/speed conversion problem

  1. Mar 5, 2010 #1
    1. The problem statement, all variables and given/known data
    The velocity of light is 1.86 x 108 mi/hr. The distance of Mercury from the Sun is approximately 5.78 x 107 km. How many minutes will it take for light from the Sun to travel to Mercury?



    2. Relevant equations
    1 mi = 1.609 km
    time = distance/speed
    60 min/1 hr



    3. The attempt at a solution
    1.609 km/1 mi * 1.86 x 108 mi/hr = 2.99 x 108 km/hr

    time = 5.78 x 107 km / 2.99 x 108 km/hr = 1.933 x 10-1 hr

    60 min/1 hr * 1.933 x 10-1 hr = 115.98 x 10-1 min

    Answer: 11.598 minutes.

    That answer does not make sense to me. What did I do wrong here?
     
  2. jcsd
  3. Mar 5, 2010 #2

    rock.freak667

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    Homework Helper

    I think you converted km to mi incorrectly.

    1 kilometer = 0.621371192 miles
     
  4. Mar 6, 2010 #3

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    Yes, so one mile is 1/.621371192 km= 1.60934400 miles which is what he used. And he was converting from miles to kilometers.

    However, Mathnomolous, the speed of light is 1.86 x 108 miles per second, not miles per hour!

    You should have divided by 60 to convert second to minutes, not multiplied to convert hours to minutes.
     
    Last edited: Mar 6, 2010
  5. Mar 6, 2010 #4
    Your speed of light is incorrect. It's not 2.99 x 108 km/hr, it's 2.99 x 108 m/s, which is something like 6.71 x 108 mi/hr or 186,000 miles per second.
     
    Last edited: Mar 6, 2010
  6. Mar 6, 2010 #5
    I typed the problem as it appears on my chemistry textbook. I also asked the professor to do the problem in class, with the same result. I never imagined the textbook had that kind of error. Thanks for the correction. I should be able to obtain the right answer now.
     
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