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Ratios of inertia

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  1. Sep 25, 2016 #1
    1. The problem statement, all variables and given/known data

    The vx(t) curves for two carts, A and B, that collide on a low-friction track are shown below:
    Mazur1e.ch4.p10.jpg
    What is the ratio of their inertias?
    2. Relevant equations
    the ratio i am looking for is mB/mA

    3. The attempt at a solution
    I believed that the ration was 1/2 however that is not correct and i do not see how there can be another ratio
     
  2. jcsd
  3. Sep 26, 2016 #2

    mfb

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    How did you get the value 1/2?
    Which mass is larger?
     
  4. Sep 26, 2016 #3
    is the cart of mass B not larger because it had a smaller change is speed, meaning it has a larger inertia and greater mass. i got the 1/2 ratio because the mass of cart A is double the mass of cart B
     
  5. Sep 26, 2016 #4

    mfb

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    Correct, cart B has a larger mass.
    This is in contradiction to what you said immediately before that.
     
  6. Sep 26, 2016 #5
    I meant cart B is double the mass of cart A. But the ratio isn't 2/1
     
  7. Sep 26, 2016 #6

    mfb

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    Why not?
    You can try to estimate the changes a bit better from the diagram, that will give a value very close to 2/1, but usually you are not supposed to measure individual pixels on problems like this.
     
  8. Sep 26, 2016 #7
    i already tried the ratio and it was wrong which is why i'm confused for the question
     
  9. Sep 26, 2016 #8
    turns out the answer was 2.1
     
  10. Sep 26, 2016 #9

    mfb

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    Okay, bad problem statement. Giving something that is so close to 2 and then expecting students to count pixels is a very bad style.
     
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