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Homework Help: Mechanics train problems

  1. Mar 18, 2006 #1
    :confused: Please help with this problem. A train moves from rest with const accel. a in a straight line. A man at distance b behind the train chases it with const. speed V. Show he can catch it if V^2 >2ab, and find when he does so.
    I have found formulas for distance travelled for each and equated these but cannot understand where the Vsquared comes from.
    Thanks to anyone who can help. Jess x
  2. jcsd
  3. Mar 18, 2006 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Hint: When you equate those distance formulas you'll get a quadratic equation. What must be true for that quadratic to have a physically meaningful solution?
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