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Homework Help: Two trains passing each other

  1. Sep 15, 2010 #1
    1. The problem statement, all variables and given/known data
    A 120m long train with a constant speed of 10.0m/s is passing by a 80.0m long train traveling at 6.0m/s on the opposite lane. How long does it take for these two train to completely pass by each other if their distance in between is 260m?

    2. Relevant equations

    3. The attempt at a solution
    Total distance Train A has to cover: 260m+80m= 340m
    Total distance Train B has to cover: 260m+120m= 380m

    Train A's Time = 340m / 10m/s
    = 34s

    Train B's Time = 380m / 6m/s
    = 63.33s

    Then im not sure what to do next but i'm given the answer of 28.8s...
    Last edited: Sep 15, 2010
  2. jcsd
  3. Sep 15, 2010 #2


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    Homework Helper

    Welcome to PF!

    Curious wording here. It WILL cover some distance while the pass is happening, and how far that is will depend on how long it takes the other train to go by. So, your formula for the distance traveled by train A should have a T for time in it. You know its speed, so you should be able to write an expression for how far it goes in time T. I wouldn't add any length or closing distance onto that. The final equation will go something like this:
    distance traveled by train B in time T = separation + length + distance traveled by train A in time T.

    Note the T's in the equation - you will be able to solve the equation for the time and get the answer to the question.
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