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Rotational motion/conservation HW problem

  1. Dec 5, 2011 #1
    A horizontal vinyl record of mass 0.10 kg and radius 0.1 m rotates freely about a vertical axis through its center with an angular speed of 4.7 rad/s. The rotational inertia of the record about its axis of rotation is 0.0005 kg*m^2. A wad of wet putty of mass 0.020 kg drops vertically onto the record from above and sticks to the edge of the record. What is the angular speed of the record immediately after the putty sticks to it?

    Did I do this correctly?? I really struggled to get this lol

    Angular momentum = moment of inertia * angular velocity
    Moment of inertia of a solid cylinder, like the record = ½ * mass * radius^2

    I = ½ * 0.1 * 0.1^2 = 0.0005
    Initial angular momentum = 0.0005 * 4.7

    Moment of inertia putty = mass * radius^2
    I = 0.02 * 0.1^2 = 0.0002

    Total moment of inertia after the sticks to the edge of the record = Sum of I’s = 0.0007
    Final angular momentum = 0.0007 * final angular velocity

    Final angular momentum = Initial angular momentum
    0.0007 * final angular velocity = 0.0005 * 4.7

    new angular velcoity = 3.36 rad/s
     
  2. jcsd
  3. Dec 5, 2011 #2

    Delphi51

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    Homework Helper

    All correct!
     
  4. Dec 5, 2011 #3
    many thanks!! I just wanted to make sure i wasnt crazy lol
     
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