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Calculate the mass of the disk?

  1. Jun 9, 2016 #1
    1. The problem statement, all variables and given/known data
    The moment of inertia of the disk-clay system about the central axis of the disk is I = 1.5 kg m2
    Disk's mass = M
    The clay's mass = 0.12 kg
    Calculate the mass of the disk?

    2. Relevant equations
    I = m r^2

    3. The attempt at a solution
    I thought that the moment of inertia may just be the sum of the individual moment of inertia's of the two objects. I know that I for a disk is equal to 1/4 MR^2, but I do not know the one for the clay.
     
  2. jcsd
  3. Jun 9, 2016 #2

    billy_joule

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    Correct.



    You sure you've interpreted the axis correctly?
    https://en.wikipedia.org/wiki/List_of_moments_of_inertia

    Was there a diagram? As it is, we don't know r disk or rclay so can't find mclay.
     
  4. Jun 9, 2016 #3
    Yes. The diagram showed a piece of clay is sitting at the rim of the disk and not sliding on the disk.
     
  5. Jun 9, 2016 #4

    billy_joule

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    Post the diagram and the entire question statement word for word, without it we're just guessing/relying on your interpretation.
     
  6. Jun 9, 2016 #5
    upload_2016-6-9_1-36-57.png

    A horizontal uniform disk with a mass M and a radius R=1.5m is free to rotate about its central axis perpendicular to the disk’s flat surface. A piece of clay with a mass m=0.12kg is sitting at the rim of the disk and does not slide on the disk. The moment of inertia of the disk-clay system about the central axis of the disk is I=1.5kgm2.At time t=0s, a constant external force, F, is applied tangentially at the rim of the disk causing the disk-clay system, initially at rest, to start rotating with a constant angular acceleration ofα=0.25rad/s2.
     
  7. Jun 9, 2016 #6

    billy_joule

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    There's doesn't appear to be a question?
    Can you follow the link in post #2 and identify the relevant MOI equations for the disk and clay?
     
  8. Jun 9, 2016 #7

    haruspex

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    Note that part of the axis specification.
     
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