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Jet is flying Physics question

  1. Nov 6, 2012 #1
    1. The problem statement, all variables and given/known data
    A jet is flying at 600 mi/h in a direction of 45 degrees North of West. 2.5 minutes later it is flying at 450 mi/h in a direction of 30 degrees North of East.
    a) Sketch a vector diagram labeling Vi, Vf, and ∆V.
    b) Calculate the average velocity vector in unit-vector notation.
    c) Calculate the magnitude and direction of average velocity


    2. Relevant equations

    average velocity = displacement/ time

    3. The attempt at a solution

    I do not know the vector of which the plane going 450mi/h while the first vector is 25miles
     
  2. jcsd
  3. Nov 6, 2012 #2

    lewando

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    "I do not know the vector of which the plane going 450mi/h..." Are you saying that you do not know how to draw this?

    "...while the first vector is 25 miles" Where does 25 miles come from?

    I think you might need some vector fundamentals training. Here is a good resource--
    http://www.physicsclassroom.com/class/vectors/u3l1a.can [Broken]

    There are tons of web sites that could help if this one is not satisfactory
     
    Last edited by a moderator: May 6, 2017
  4. Nov 6, 2012 #3
    I know how to draw it, but I do not know how to solve it.

    600mi/h *2.5min = 25miles
     
  5. Nov 6, 2012 #4

    lewando

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    Good, so then you can answer part a). If you can, please attach your drawing.

    Okay, what I meant was "25 miles" is not a vector and even so it is not relevant to any of the questions.

    To quickly be able to help you, you need to indicate specifically what it is you are having trouble with. Which of the following are having trouble with (check all that apply)

    [ ] average velocity vector definition
    [ ] unit vector notation
    [ ] determining the magnitude of a vector
    [ ] determining the direction of a vector
     
    Last edited: Nov 6, 2012
  6. Nov 6, 2012 #5

    PhanthomJay

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    That is correct, so I don't know how you can find the average velocity based on the given data, since the time for the 2nd part of the journey is not stated, and therfore, you cannot calculate the displacement. Did you leave something out of the problem statement?
     
  7. Nov 7, 2012 #6

    lewando

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    I was thinking this was solvable if you assume constant acceleration.
     
  8. Nov 7, 2012 #7

    PhanthomJay

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    Unless the problem left out some data, it may have been assuming the same thing. But you just can't add up the two velocities and divide by two to get the average velocity unless the plane flies in a straight line with constant acceleration, which is far from the case here, so you need to know or find the total displacement, which cannot be determined with the given info. I guess only the OP knows for sure....the change in velocity is another matter, that is calculable.
     
  9. Nov 7, 2012 #8

    lewando

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    Without giving too much away, and if the OP can confirm (or is willing to assume) constant acceleration, consider:

    vf = vi+ at
    vf - vi= at = Δv

    If you choose the origin as the point where the plane begins its constant acceleration phase (ri = 0)

    then rf= vit + 0.5at2
     
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