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Finding the Mass from an Acceleration vs Force graph

  1. Jul 28, 2014 #1
    I have to confirm newtons 2nd law via a track and trolley experiment

    1. The problem statement, all variables and given/known data

    The trolley’s mass is kept constant.
    The weight of the cart (252g) plus two bar weights (500g) is = 752 grams, plus additional weights of either, 10g, 15g, 20g, 25g or 30g for the different trials.

    The acceleration weights are:
    25g
    20g
    15g
    10g
    5g
    for the different trials.

    This is what i got in the end...

    Acceleration mass (g)--------Force (N)-----------Average acceleration ms-2

    ---------5-----------------------0.049---------------------0.10
    ---------10----------------------0.098---------------------0.22
    ---------15----------------------0.147---------------------0.36
    ---------20----------------------0.196---------------------0.44
    ---------25----------------------0.245---------------------0.63


    2. Relevant equations

    F=ma


    3. The attempt at a solution

    I plotted an acceleration vs Force graph, which gave me slope=2.6. And I thought that since F=ma, then the slope would be 1/m = 1/2.6 =0.3846... kg.
    If i’m thinking correctly then this should be the value for the mass of the trolley (the cart+the bar weights+the additional weights+acceleration mass)

    But when i add all of the components of the trolley’s mass i get 787g...which is nowhere near 0.3846... kg.

    I’m not sure what i’m doing wrong, or if I’m going about solving this in completely the wrong way. Or maybe i made a big error during the experiment?
     
  2. jcsd
  3. Jul 28, 2014 #2
    No, but it's pretty near 2 x 0.3836 kg. How did you get the acceleration?
     
  4. Jul 28, 2014 #3
    We used a motion sensor which took the velocity/time for each trial. the Average acceleration I posted there is the average of 5 trials for each of the different acceleration masses.
     
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