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Homework Help: Constant acceleration problem involving trains

  1. Sep 3, 2009 #1
    I'm having trouble with this problem mostly because I can't think of the logic behind it, so I don't know which of the basic formulae to use. Excuse my "noobieness" as I'm a first-year physics student.

    The question states, "Two trains face each other on adjacent tracks. They are initially at rest, and their front ends are 39 m apart. The train on the left accelerates rightward at 0.91 m/s^2. The train on the right accelerates leftward at 1.19 m/s^2. How far does the train on the left travel before the front ends of the trains pass?"

    So far, I've tried to do the problem manually by subtracting both trains' movements from the total 39m, but that is very inefficient and hard to get perfectly. Can anyone give me a push in the right direction? I feel like this should be easy, I'm just having a momentary brainfart.
  2. jcsd
  3. Sep 3, 2009 #2
    Think of their accelerations relative to each other. A lot of times you will get situations where you have to consider two bodies in motion. These situations become easier to grasp when you consider one to be at rest and the other to be moving relative to it.

    On the side, however, remember to note that Newton's laws apply only to non-accelerating reference frames.
  4. Sep 3, 2009 #3


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    Homework Helper

    The trains start from rest. When they meet they must have traveled for the same time interval t. During that time one train, let one train travels x m. Then what is the distance traveled by the other train?
    Write down the kinematic equation which shows the relation between initial velocity, acceleration, time and displacement.
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