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Homework Help: Finding distance using vector components

  1. Oct 11, 2009 #1
    1. The problem statement, all variables and given/known data


    With reference to Fig. 3 (not accurate), where the origin is at the centre of the image, if r1 = (0.10)î+(-0.80)j hat, and r2 = (-0.90)î+(0.10)j hat, what is the distance between the dots?

    2. Relevant equations


    3. The attempt at a solution

    I'm not so good with these i hat and j hat vector components. I've tried using (x2-x1) + (y2-y1) but that didn't give the correct answer. I'm not really sure what I can do with the two equations.
  2. jcsd
  3. Oct 11, 2009 #2
  4. Oct 11, 2009 #3
    That is a helpful link, however I still can't get the answer. XD Do I have to find the angle between r1 and r2 and use that to find the distance or does it have to do with the addition of the i hat components and the j hat components?
  5. Oct 11, 2009 #4
    the beauty of unit vectors is that it already takes the angle into consideration! all you have to do in this case is add the i vectors with i vectors and js with js.
  6. Oct 11, 2009 #5
    I've tried that but BLS/CAPA is still telling me that my answer is wrong. Maybe I'm entering it wrong...?
  7. Oct 11, 2009 #6
    The distance between two points is the magnitude of the vector connecting these two points. In your problem this vector is [tex]\vec{r} = \vec{r_{2}}-\vec{r_{1}}[/tex]. To encounter the magnitude of this vector, all we have to do is calcute the scalar product of it with itself and take the square root. So,
    [tex]distance = \sqrt{\vec{r}\dot\vec{r}}[/tex].
  8. Oct 12, 2009 #7
    Thank you! I have the answer now. =D
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