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Homework Help: Angular momentum Homework Problem

  1. Apr 6, 2005 #1
    This is a problem I'm having a world of problem with:

    A. What is the angular momentum of a 2.56 kg uniform cylindrical grinding wheel of radius 17.5 cm when rotating at 1480 rpm?

    Correct: 6.08 kg*m^2/s

    B. How much torque is required to stop it in 6.50 s?

    So after 5 tries, I get that Torque = Moment of Inertia * Alpha.

    Alpha = Delta (w)/ Delta (t)
    Then I = 1/2*m*r^2
    and I get .9347 N*m, but the computer does not. Any suggestions as to what I am doing wrong?
    Last edited by a moderator: Mar 7, 2013
  2. jcsd
  3. Apr 6, 2005 #2


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    U've given it 4 sign.digits cf.3 before...:tongue2:

    If A is correct (manipulating units),then B is correct,as well.I don't c what it could be.

  4. Apr 6, 2005 #3
    Well I have lot of these homework questions. Heres another one that I cant figure out.

    An Atwood machine consists of two masses, m1 = 6.80 kg and m2 = 8.55 kg, connected by a cord that passes over a pulley free to rotate about a fixed axis

    Then theres a picture but I dont know how to link to it. Its just 2 weights on the end of a string around a pully.

    The pulley is a solid cylinder of radius R0 = 0.535 m and mass 0.771 kg. Determine the acceleration a of both masses. Ignore friction in the pulley bearing.

    10. [1pt]
    What percentage error in a would be made if the moment of inertia of the pulley were ignored? Do not enter units.

    Any ideas on there either? I did the same kinda thing and said T = F*R=I*Alpha etc etc
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