1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Two vectors

  1. Jul 30, 2009 #1
    Two particles move through space in a way that at time t, they are traveling in directions

    (t-6,-t,6) And (1,2,1-t)
    at what time are their directions parallel?


    I know that for them to be parallel, a = Kb, where a and b are the two vectors, and one vector is a scalar of the other

    I get something along the lines of

    (t-6,-t,6) = K(1,2,1-t)
    giving me equations
    t-6 = k
    -t = 2k
    6 = k(1-t)

    please someone check

    I had -t = 2k
    (-t/2) = k

    subbing into t-6

    t-6 = (-t/2)
    2(t-6) = -t
    2t - 12 = -t
    3t = 12
    12/3 = t

    is this right?
  2. jcsd
  3. Jul 30, 2009 #2


    Staff: Mentor

    This is easy to check. Substitute t = 4 into your two vectors. If this value of t is correct, one vector will be a scalar multiple of the other (and vice versa, but the scalar multiple in this case will be the reciprocal of the other).
  4. Jul 30, 2009 #3
    so it's right?
  5. Jul 30, 2009 #4


    Staff: Mentor

    What does your check show?
  6. Jul 30, 2009 #5

    -2=k*1, k = -2
    -4=k*2 k = -4/2 = -2
    6=k*(-3) k = 6/(-3) = -2

    so yeah

    awesome sauce
    cheers bigears
  7. Jul 30, 2009 #6


    Staff: Mentor

    Good work! And you did it all yourself!
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Two vectors
  1. Two vector problems (Replies: 6)