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Turning a vector into a vector function of time

  1. Dec 31, 2014 #1
    1. The problem statement, all variables and given/known data

    A Velocity vector: V = (12,4)

    write the vector as a vector function of Displacement.

    2. The attempt at a solution

    I integrated the components of the Vector and got the function S(t) = (S(12t), S(4t))

    I this correct at all?
     
  2. jcsd
  3. Dec 31, 2014 #2

    Ray Vickson

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    This cannot be answered because the notation S(12t), etc., is undefined.
     
  4. Dec 31, 2014 #3
    why?
     
  5. Dec 31, 2014 #4

    Ray Vickson

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    Why what?
    (1) Why the notation is undefined? The answer is: because you have not defined it.
    (2) Why I can't answer the question? Because---as I have already said---I have no idea what you mean by what you wrote.
     
  6. Dec 31, 2014 #5

    Mark44

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    Do you mean S(t) = <12t, 4t>?
    If so, don't forget you need the constant of integration.
     
  7. Dec 31, 2014 #6
    Ray, I asked why because I literally have no idea what I'm talking about.

    Mark, from V = 12x + 4y, am i allowed to turn it into that function that you wrote.
     
  8. Dec 31, 2014 #7

    mfb

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    Is this the exact and full problem statement? It sounds a bit odd.
     
  9. Dec 31, 2014 #8
    I made it up myself.
     
  10. Dec 31, 2014 #9

    mfb

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    I don't think it makes sense.
     
  11. Dec 31, 2014 #10

    Ray Vickson

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    You say you literally have no idea what you are talking about. So, let's look at that.


    If you are told a function f(t) for x-displacement, say x = f(t), can you figure out from that how to obtain velocity? Can you go backwards: given a velocity function g(t), so that v = g(t), can you figure out from that how to get displacement x = f(t)? [In a nutshell, that is what you are being asked to do in this problem.]


    If the answers to both (or even one) of these questions is NO, you need to upgrade your background. You can Google “displacement and velocity” to find numerous articles on these issues.
     
  12. Dec 31, 2014 #11
    Wait a minute.

    I can breakup the vector into:

    Vx = 12

    and

    Vy = 4

    these can easy be described as a function. a constant function of velocity. I can find the integral of the function V(t) = 12, and turn it into S(t) = 12t
     
  13. Dec 31, 2014 #12
    and furthermore, from S(x) = x, which is a function of displacement, I CAN find the function for instantaneous velocity by simply finding the derivative. The answer is, it has no velocity as the function is constant.
     
  14. Dec 31, 2014 #13

    Mark44

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    You could have V(t) = 12i + 4j, which would be the same as V(t) = <12, 4>. i and j are the unit vectors in the direction of the positive x- and y-axes.
    Is this a different example? Above you have Vx = 12, and now you have V(t) = 12. This would be incorrect if V(t) = <12, 4>.

    If you really mean Vx(t), the x-component of velocity, then Sx(t) = 12t + C1. As I said before, you have to add the constant of integration.

    This makes no sense. If you're talking about displacement and velocity, the independent variable should be t, not x. Having said that, if S(x) = x, then S'(x) = 1 represents the "velocity" here, a constant velocity, which is not the same as "no velocity."
     
  15. Dec 31, 2014 #14
    I get what your saying. S(x) = x was meant to be a position function. The point is i wanted to turn the velocity vector into a function. that's all. I didn't know if that's even possible.
     
  16. Dec 31, 2014 #15

    Mark44

    Staff: Mentor

    V(t) = <12, 4> is a vector-valued function, albeit one that produces a vector constant. Or in slightly different form, V(t) = 12i + 4j.
     
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