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Homework Help: Acceleration Problem due to Rotational Inertia [Exam in 9hrs!]

  1. Dec 17, 2007 #1
    [URGENT] Acceleration Problem due to Rotational Inertia [Exam in 9hrs!]

    yes i know i might be late but i hope somebody can help me out with this problem because i cant figure it out. Exact word for word:

    A block of mass m2= 12kg hangs from a rope. The rope wraps around a pulley and then attaches to a second block of mass m1=8kg, which sits on a frictionless table. The radius of the pulley is .10m and its rotational inertia is I=.040 kg-m2. What is the acceleration of the blocks when they are released.

    here is how it looks:


    a modified atwood machine.
  2. jcsd
  3. Dec 17, 2007 #2
    You essentially need to draw 3 free body diagrams. Use Newton's Second Law to set up the equations for the two blocks, and Newton's Second Law for rotational motion, [tex] \Sigma \tau = I \alpha [/tex] to set up an equation for the net torque on the massive pulley. Also note, you'll want to use the rolling constraint [tex] a = r \alpha[/tex] to get the angular acceleration in terms of "a." Does this help?
  4. Dec 17, 2007 #3
    sort of i was using
    m=12kg + 8kg

    but its not one of the choices which are:
    a. 3.5
    b. 3.9
    c. 2.5
    d. less than 2.5
    e. cannot be determined
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