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Homework Help: Vectors help? How do I find a constant of this vector?

  1. Feb 11, 2009 #1
    The vector is this:

    V=(5i-j)+q(i+4j) and it is in the direction of north-east.

    I have to find the constant (q) of this vector. The part of the question before this showed that if a vector of ki+kj, where k was a positive constant is a vector of magnitude k(square root)2. So I don't know whether I have to use that in part of this answer.

    I really have no idea where to start or what to do because I don't know what V is. But I was thinking about the direction, so do I have to adjust the q so that the angle is 45 degrees?

    Any help at all would be greatly appreciated. Thanks.
  2. jcsd
  3. Feb 11, 2009 #2


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    Homework Helper

    Welcome to PF.

    First I think you would want to rearrange the coefficients wouldn't you?

    V = (5+q) i + (4q - 1) j

    Next they tell you that the direction is Northeast.

    That suggests that the coefficients of i and j are equal doesn't it?

    So ...

    If you wanted to find |V| (magnitude of V) then you would use what they showed with the k i + k j example.
  4. Feb 11, 2009 #3
    Thankyou so much!

    So from that, I've managed to get q= 2.

    (5+q)i = (4q-1)j

    Is this right?
    Thanks again!
    Last edited: Feb 11, 2009
  5. Feb 11, 2009 #4


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    Homework Helper

    Looks right to me.
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