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Intersection/Collision of two lines in R^3

  1. Feb 6, 2011 #1
    1. The problem statement, all variables and given/known data

    Determine whether r1 and r2 collide or intersect:

    r1(t) = <t^2 + 3 , t + 1 , 6t^-1 >

    r2(t) = <4t , 2t -2 , t^2 - 7>

    I am completely lost in this problem and was hoping for a just a hint at where to begin. I'm unsure what it even means if two lines collide or intersect.

    I've done a similar problem that read:

    Determine if

    r1(t) = < 1 , 0 , 1 > + t<3, 3, 5 >

    and

    r2(t) = < 3, 6, 1 > +t<4, -2, 7>

    intersect.

    I did it by multiplying the scalars out and adding the two vectors. Then setting the x components of the two lines equal to each other...same with y and z. This gives me three equations with which i use to solve for t1 and t2. Finally, plugging the t values into the third equation will prove whether or not the lines intersect if the equation is satisfied with the two t values.

    I'm unsure what 'collision' is. Do i approach this problem the same way?

    Thanks all
     
  2. jcsd
  3. Feb 6, 2011 #2

    Dick

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    Yes, do it the same way for intersect. 'Collide' I think means that they intersect with the same value of t in each equation. I.e. they are at the same place at the same time.
     
  4. Feb 6, 2011 #3
    so if i find the value for t1 to be 3 and the value for t2 to be 3 and they satisfy all equaitons for x, y and z then these lines collide because both "t" values are the same and all intersections are the same?
     
  5. Feb 6, 2011 #4

    Dick

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    Yes, t=3 is a collision. There MIGHT be more intersections that aren't collisions. But in this case I don't think there are.
     
  6. Feb 6, 2011 #5

    Dick

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    Yes, t=3 is a collision. There MIGHT be more intersections that aren't collisions. But in this case I don't think there are.
     
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