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Relative Motion- Airplane/Wind

  1. Feb 13, 2013 #1
    1. The problem statement, all variables and given/known data

    A jetliner has a cruising air speed of 620mph relative to the air.

    Part B
    How long does it take this plane to fly round-trip from San Francisco to Chicago, an east–west flight of 2000 miles each way, if the wind is blowing at 120mph from the west to the east?




    2. Relevant equations



    3. The attempt at a solution

    I've tried 8 hours.
    and 7.225 hours.
     
  2. jcsd
  3. Feb 13, 2013 #2

    tms

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    Show us your work, or we can't tell where, if anywhere, you went astray.
     
  4. Feb 13, 2013 #3
    i did

    620-120= 500

    so that makes 4000/500= 8 hours


    for 1 other

    it only affects 1 trip

    so 2000/620= 3.225

    2000/500= 4

    so trip time = 7.225

    both answers wrong
     
  5. Feb 13, 2013 #4

    tms

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    The wind affects the trip in both directions: it helps in one direction and opposes in the other.
     
  6. Feb 13, 2013 #5
    620 + 120 one-way = 740
    620 - 120 one-way = 500

    2000/740 mph = 2.70
    2000/500 mph = 4



    = 6.7 hours


    is that correct
     
  7. Feb 13, 2013 #6

    BruceW

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    Homework Helper

    hi there, welcome to physicsforums. I'm guessing your assumption is that the wind velocity and cruising velocity 'add up' to get the true speed. Since they don't give you any other information, then this does seem like the right way to do it.

    I get a different answer to you though. Remember that since he is doing a two-way flight, that on the way there, the plane is going against the wind, and with the wind on the way back.

    EDIT: lol, I only saw your first post when I wrote this. And yes, I also get an answer of 6.7 hours
     
  8. Feb 13, 2013 #7

    I posted some new work, is that what you got?
     
  9. Feb 13, 2013 #8

    BruceW

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    Homework Helper

    yep! nice work :)
     
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