1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    Science Advisor
    Homework Helper

    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
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook