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Homework Help: Conservation of Momentum Lab

  1. May 9, 2009 #1
    So, here is my data:
    MASS OF CAR 1 7.5 N 7.5 N 7.5 N
    MASS OF CAR 2 7.5 N 7.5 N 7.5 N
    TIME FOR CAR 1 (s) 8.63 8.31 9.40
    TIME FOR CAR 2 (s) 7.50 10.72 8.78
    DISPLACEMENT FOR CAR 1 (m) 305.00 365.00 348.60
    DISPLACEMENT FOR CAR 2 (m) 387.50 369.10 305.10

    And the questions from the lab are:
    1. Find the velocity of each car after the collision. Remember it is
    accelerating from rest.
    2. Find the momentum for each car before and after the collision. Then find
    the total momentum before the collision and the total momentum after
    the collision. p1 + p2 = p1+ p2
    3. Determine the % difference for the four different situations.

    (The lab consisted of two cars placed side by side, when a button was pushed on one car a rod would extend and cause a collison, I hope that made sense!)

    My issues:
    -I kind of get the feeling from the first question that I may have used an incorrect approach in solving this, but I just divided the displacement by the time. (ex. 385.50m/7.50s=51.7m/s)
    -Okay, for the second question, I would use p=mv to find the momentum. But wouldn't the momentum before the collision always be zero since it begins from rest? so wouldn't it end up looking like 0 = (whatever the added momentums after the collisons are)? meaning momentum is not conserved? I thought momentum was always conserved but maybe I am completely wrong.
  2. jcsd
  3. May 9, 2009 #2


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    Homework Helper

    The cars move in opposite directions don't they?
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