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Mistake Kinematics Problem

  1. May 18, 2014 #1
    Please look at pictures.

    Why is it that they use 24 seconds for the time in b)? They get t=6.16s, why do they not plug that into the Dx equation to get 185m of x displacement?
     

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  2. jcsd
  3. May 18, 2014 #2

    Doc Al

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    Looks like a mistake.
     
  4. May 18, 2014 #3
    DocAl, is the speed also wrong in this problem? I think they made a mistake right at the end. They forgot to square root?
     

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  5. May 18, 2014 #4

    Doc Al

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    You are right. They made a mistake.

    What book are you using?
     
  6. May 18, 2014 #5
    It's a bunch of review problems my teacher sent me "at our own risk."

    But, since I'm not really an ace in physics, I try to confirm the mistakes as much as possible.
     
  7. May 18, 2014 #6
    Another mistake spotted?

    They made a mistake with the *10^4. Should be 10^3. Angles do not change (they are good).
    The final velocity should be 12.07m/s, IE 43.45 km/h.

    By the way, should we not express scientific notation with only numbers from 1 to 9? Why do they put 10.1 x 10^4 etc...?

    I'll refer this page to my class. They'll be glad :)
     

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  8. May 18, 2014 #7

    Doc Al

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    I guess he didn't double check them for errors.

    Good idea. It's good practice.
     
  9. May 18, 2014 #8

    Doc Al

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    Yes, another mistake.

    As long as they do it right, it doesn't really matter. (Though you are correct.) But that's their first mistake: The momentum values are off by a factor of ten: they have 29.2 x 10^4 instead of 2.92 x 10^4, etc.

    Good!
     
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