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Homework Help: Relative velocities

  1. Mar 15, 2010 #1
    1. The problem statement, all variables and given/known data
    The wind is blowing at 72km/h south relative to the earth, and a plane is traveling 320km/h (28 degrees south of west relative to the wind) directly above a city. give displacement from the city in 2h time


    2. Relevant equations
    Plane is P wind is W earth is E

    VPW=VPE+VWE



    3. The attempt at a solution

    re arrange to find that
    VPE=VPW-VWE
    VPE=248km/h

    The only thing I dont understand is how to determine the new angle of the plane to the earth...
     
  2. jcsd
  3. Mar 15, 2010 #2

    rl.bhat

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    Homework Helper

    Velocities are vectors. You cannot add or subtract them directly.
     
  4. Mar 15, 2010 #3
    Hi slpnsldr. Your formula was incorrect. It should look like this
    [tex]\vec{_{p}V_{E}}=\vec{_{p}V_{w}}+\vec{_{w}V_{E}}[/tex]

    Notice when you add these relative velocities, the subscript "w" cancel each other out. And that is the only trick to it.
     
  5. Mar 15, 2010 #4
    ok, ive figured out my displacement.. but im still unclear about how to find the planes new angle
    somethign to do with the sine law?
     
  6. Mar 15, 2010 #5
    Oh, that might be hard to explain without a diagram. Maybe you need to include a diagram.
     
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