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Homework Help: Graph of a cart in motion using ticker tape

  1. Apr 5, 2010 #1
    1. The problem statement, all variables and given/known data
    Ok this is more of a problem Im having within a lab exercise. The scenario is this, I have a cart attached to a string that is attached to a mass of 100g hanging off the ground with a pulley.. So the cart is on a table, the string goes upwards, hooks around a pulley and goes downwards attached to a mass. I have ticker tape showing the motion of the cart then using time and displacement, I got velocity using v = d/t, and the data is as follows:
    Time Speed
    1 5.3
    2 6
    3 7.3
    4 8.8
    5 10.5
    6 12
    7 15
    8 18
    9 21

    2. Relevant equations
    v = d/t

    3. The attempt at a solution
    My problem is, that the teacher stated "It should be non-linear and resemble a root curve because the acceleration is not constant." However, when I graph this, the v-t graph is a straight line meaning that the acceleration is constant! To me, it makes sense that the acceleration is constant because there is a constant mass pulling on the cart with a constant force, the angle but my teacher says its not. Now I can easily change my data to whatever I want it to, my teacher has no problem with that, however I don't know what a root curve is supose to look like? is it like the graph of y = root(x) or is it more like y = 2^x?? Or maybe im missing something and the data i have is right? i dont no, please help
  2. jcsd
  3. Apr 6, 2010 #2
    The data you have given is definitely not a straight line graph.
    between the 1st two values the difference is 6-5.3= 0.7
    between the last two values it's 21-18 = 3
    This will not give a straight line graph.
    Is your data actually displacement against time? (Not velocity?)
    The displacement against time graph will look like that.
    In order to find the velocity of the cart, you need to do a calculation on the dots from the ticker tape. It's not read off directly.
    If you have just read off directly from the tape, I'm certain that what you have measure is displacement, not velocity.
    How did you find velocity?
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