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Homework Help: Moment of Inertia/Torque Question

  1. Jul 10, 2007 #1
    The combination of an applied force and a frictional force produces a constant torque of 34 N.m on a wheel rotating about a fixed axis. The applied force acts for 9.1s, during which time the angular speed of the wheel increases from 0 to 16 rad/s.

    a)What is the moment of inertia of the wheel?

    If the applied force is removed, the wheel comes to a stop in 73s.

    b)What is the frictional torque?

    c)How many revolutions does the wheel make during the entire 82s interval?
  2. jcsd
  3. Jul 10, 2007 #2


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    Homework Helper

    first you may want to identify some potentially useful formulas or concepts
  4. Jul 10, 2007 #3
    Well torque= moment of inertia X angular acceleration....but how do u get angular acceleration if you dont know the radius??
  5. Jul 10, 2007 #4
    I figured out moment of inertia, but is it the same value to use when you are trying to get frictional torque??
  6. Jul 10, 2007 #5
    This problem looks so familiar. This might be random, but you don't happen to be in Dr. Turner's class?
  7. Jul 10, 2007 #6
    yeah...this homework has really been giving me problems. i just want to finish. any help would be nice. its always good to have extra help from other people in the class
  8. Jul 10, 2007 #7
    lol what a coincidence. I got part a and b, but c I'm just lost. Wait till you look at HW 24...it's a killer I just wanna shoot myself in the head.
    For part A, use that equation Torque = mr^2 x acceleration.
    You know the torque...for acceleration just take 16/9.1...plug those values in...and you are left with mr^2, which is the moment of inertia.
    For part B, apply the kinematics equation...wf= w0 + at, find the acceleration, and plug it into Torque = mr^2 x a.
  9. Jul 11, 2007 #8
    but for this question u aren't given a radius. i need q15 on hw 23 (part b)...for part a i did torque= I x angular acceleration and i got it right like you said....

    for part b...how do i do it? i get what you are saying...but it says the wheel comes to REST after 73 seconds.. so if u do the kinematics equation wf=wo + at, wouldn't wf be zero?? how do u calc that??

    sorry i know you're busy w/ hw 24 i just really wanna do this one before the 2am cutoff
  10. Jul 11, 2007 #9
    it's okay,
    set wf = 0 and w0 = 16, and t = 73. solve for a, which sould be a negative #.
  11. Jul 11, 2007 #10
    Thanks!!! if i get q16 ill let u know...i can't seem to figure it out either...i hate to bug u but how did u figure out question 18 about the velocity of the wheel?? i got 17 but i dont know how to do number 18. please let me know...i haven't answered very many questions on this hw
  12. Jul 11, 2007 #11
    AIM me...Sherry22
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