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Homework Help: Velocity Formula

  1. Feb 17, 2008 #1
    [SOLVED] Velocity Formula

    1. The problem statement, all variables and given/known data
    "Runner A is initially 6.0km west of a flagpole and is running with a constant velocity of 9.0km/h due east. Runner B is initially 5.0km east of the flagpole and is running with a constant velocity of 8.0km/h due west. What will be the distance of the two runners from the flagpole when their paths cross? (Leave answer in km)"

    2. Relevant equations
    Solve this only using V = d / t

    3. The attempt at a solution
    I've tried too many.
  2. jcsd
  3. Feb 17, 2008 #2
    well first you need to find when their paths cross. This is when the sum of their individual distances is equal to 11 (the distance between them). Once you have this time you can figure out how far each person ran in that time because you have their velocities.
  4. Feb 17, 2008 #3
    Here's what I did.
    Set up a co-ordinate axis with your runners on the x-axis and flag pole at origin.
    Now express the distance each runner runs in terms of the original distance from the flag pole given and the equal final distance [tex]d_f[/tex].
    Once you have this see if it doesn't pop out at you.
  5. Feb 17, 2008 #4
    D1 would be the position of Runner A; D2 would be the position of Runner B.

    |D2 - D1| = 11

    I don't know what to do from here.
  6. Feb 17, 2008 #5
    if you think about it runner a runs 9kms in an hour and runner b runs 8kms in an hour.

    9t+8t=11 gives you a way to find when they pass eachother
  7. Feb 17, 2008 #6
    Okay, I've figured it out. I solved for D in the equation I gave and got the answer. Before, for some unknown reason, I simply could not figure it out. Thanks!
    Last edited: Feb 17, 2008
  8. Feb 17, 2008 #7
    Both ways work, spoon's may be a bit easier:tongue:.
  9. Feb 17, 2008 #8
    It is essentially the same thing.
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