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Homework Help: Linear acceleration and angular acceleration

  1. Jun 28, 2010 #1
    1. The problem statement, all variables and given/known data

    How do I solve for linear acceleration or angular acceleration without one or the other?
    I am given the mass of the object (a yoyo), the inner radius, the outer radius, and Icm (moment of inertia at the center of mass).

    Attached in a picture of the problem.

    2. Relevant equations

    a=alpha *r
    alpha=a/r


    3. The attempt at a solution
     

    Attached Files:

  2. jcsd
  3. Jun 28, 2010 #2

    rock.freak667

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    The weight of the yo-yo produced a torque τ and if you did not know, τ = Iα, since you are given 'I', you can get 'α' and hence 'a' using your relevant equations.
     
  4. Jun 28, 2010 #3
    How do you figure out the weight? Also the equation I have in my notes from the lecture, which I just double checked, is torque = I * alpha. Not I * a.
     
  5. Jun 28, 2010 #4

    rock.freak667

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    α = angular acceleration
    a = linear acceleration


    Weight is just 'mg'
     
  6. Jun 28, 2010 #5
    I do not know if I am misunderstanding you or what, but that is not the correct answer.
     
  7. Jun 28, 2010 #6

    rock.freak667

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    What did you have ?
     
  8. Jun 28, 2010 #7
    i have torque is m*g*the outer radius = I* alpha but the answer I got was 651.7 alpha which does not make any sense for a yoyo.
     
  9. Jun 28, 2010 #8

    rock.freak667

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    Can you post the values? Also the weight does not act there, it acts at through the center. So the weight is right at the start of the inner radius. So you used the wrong radius to get the torque.
     
  10. Jun 28, 2010 #9
    A yoyo with a mass of m = 179 g.
    The inner radius of the yoyo is r = 2.60 cm, and the outer radius is R = 3.60 cm
    ICM = 9.70×10-5 kgm2
     
  11. Jun 28, 2010 #10

    rock.freak667

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    Using the smaller radius does not give the correct answer?
     
  12. Jun 28, 2010 #11
  13. Jun 28, 2010 #12

    rock.freak667

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    I now read that your inertia is at the center not where it rotates.

    You need to use the parallel axis theorem I=Icm +md2 to get the inertia about the point where it rotates and then use the torque.
     
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