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Homework Help: Calculate the time required in millions of years for one orbit.

  1. Aug 3, 2010 #1
    1. The problem statement, all variables and given/known data

    The solar system is situated 26,000 light years from the centre of our galaxy, the Milky Way, and it orbits the centre at a speed of 220 km/sec.

    Calculate the time required in millions of years for one orbit.
    (NOTE: The circumference of a circle = 2 pi r where r is its radius.)

    2. Relevant equations
    3. The attempt at a solution
    I am not really sure how to do it, please help thanks
     
  2. jcsd
  3. Aug 3, 2010 #2

    tiny-tim

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    welcome to pf!

    hi quah13579! welcome to pf! :smile:

    (have a pi: π :wink:)

    find how to convert light years into km, and then calculate the length of the circumference of the orbit …

    what do you get? :smile:
     
  4. Aug 3, 2010 #3
    Re: welcome to pf!


    9,460,730,472,580.8(light-year in km) * 26000(of light-years around) * 2 * 3.1415926535 = 1545531590213152572.8104183193436(km) / 220(km/sec) / 60(sec/min) / 60 (min/hrs) / 24 (hrs/days) / 365.25(days/years) = 222613367.04559 years
    is it right?
     
  5. Aug 3, 2010 #4

    tiny-tim

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    hmmm … never never never use all those figures (you'll lose marks in the exam if you do) … 3 sig figs should usually be more than enough

    and the question asked for the answer in millions of years :rolleyes:

    but apart from that (and i haven't checked your lightyear/km figure), that looks fine :smile:
     
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