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Homework Help: Conservation of Momentum in Collisions. Help with plots!

  1. Aug 17, 2011 #1
    1. The problem statement, all variables and given/known data

    This is an experiment involving colliding 2 gliders on an airtrack. Initial and final speeds are both recorded. I need to plot a graph that proves the Conservation of Momentum holds true, but I can't seem to get the correct Y and X axis variables. Assuming both masses m1 and m2 are known, how do I go about doing this?

    2. Relevant equations

    m1v1i + m2v2i = m1v1f + m2v2f

    3. The attempt at a solution

    This only thing I can think of is manipulating the equation so it looks like:

    v2f = (m1/m2)(v1i - v1f) + v2i

    Thus I'll be taking v2f as my Y-axis, v1i - v1f as my X-axis. However, my constant is the variable v2i, so this model will probably not work...

    I'd appreciate all the help given, and thanks.
  2. jcsd
  3. Aug 17, 2011 #2


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    Well, both of the initial velocities are constants.
    So in your equation, y-axis is [itex]V_{2f}[/itex] and the x-axis is [itex]V_{1f}[/itex]. So the graph would show how the velocity of one glider depends on the velocity of the other.
  4. Aug 17, 2011 #3
    I will be repeating this experiment 5 times, getting different initial speeds each time.

    Can it still be graphed the same way, since vis will be different each time?
  5. Aug 17, 2011 #4


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    Well, for each repeat of the experiment, you could draw a different line on the graph.
    Hopefully each of these lines will have the same gradient, but will intercept the axis in different places.

    Edit: actually, If you are only recording the final velocities once for each experiment, then what I've said here won't be helpful, since you wouldn't get several lines, just points.
  6. Aug 17, 2011 #5


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    maybe instead you could calculate [itex]m_1V_{1i}+m_2V_{2i} - m_1V_{1f} - m_2V_{2f} [/itex] for each experiment (which should be about zero) and use this as the y axis, and use experiment number as your x-axis. So then you should get 5 points, which should be roughly on the x axis.
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