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Homework Help: Angular Acceleration Help Needed!

  1. Apr 25, 2004 #1
    I missed a week of school because of a virus. During that week, I missed taking a lot of physics notes. When I returned, I received a problem from my teacher that he wants me to solve. I have the notes now but I don't understand them because they weren't taught to me, so may someone please help me with doing this problem.

    1) a) Determine angular acceleration of a wheel, which has a velocity of 200 rad/min after rotating for 1.5s from start.
    b) If the wheel has a rotational inertia of 5500 kgm2(squared), what would be its radius if 5000 N of forced had been applied?
    c) If the same wheel, having reached a final velocity of 200 rad/min, were slowed down with a constant torque of 10,000 NM applied (with same radius), how long would it take to stop the wheel?
    d.) How much force was applied?
    e.) Determine the mass of the wheel. (the wheel is a solid disk)

    Again, your help would be greatly appreciated.
  2. jcsd
  3. Apr 25, 2004 #2


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    1a) Assume constant acceleration from rest state
    1b) How are torques related to angular accelerations?
    1c) as in 1b)

    e) How can you relate moment of inertia to mass?

    1d) How is torque in 1c) related to force?
  4. Apr 25, 2004 #3
    Ok, heres what I'm thinking.

    a.) (200/60)rad/min = (10/3)rad/s
    Angular Acceleration = (dW/dT)
    (3.33rad/s)/(1.5s) = 2.22 rad/s^2

    b.) I = MR^2 F = Ma
    5000N = (M)(2.22rad/s^2)
    M = 2252.25 kgm/rad

    I = MR^2
    (5500kgm^2) = (2252.25kgm/rad)(R^2)
    R = 1.56 m/rad

    c.) No idea. Please Help
    d.) No idea. Please Help
    e.) No idea. Please Help
  5. Apr 25, 2004 #4
    Maybe for part C I can do this........

    Angular Displacement = (W^2-Wo^2)/(2*Angular Acceleration)
    = (11.11rad^2/s^2)/(4.44rad/s^2)
    = 2.5 rad
    Angular Displacement = (t/2)(Wo+W)
    =(2.5 rad) = (t/2)*(10/3rad/s)
    =(2.5 rad)/(3.33rad/s)
    = .75s = (t/2)
    t = 1.5 s

    Now, I think I solved that part, but I didn't end up using Torque or the Radius, so my answer could be wrong. Please reply with any comments
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