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Homework Help: Moment of Inertia Problem

  1. May 9, 2009 #1
    1. The problem statement, all variables and given/known data

    A wheel, with circumference 0.6 m and moment of inertial 43 kg m2 about its center, rotates about a frictionless axle with angular velocity 13 radians per second. A brake is applied which supplies a constant force to a point on the perimeter of the wheel of 9 N, tangent to the wheel and opposing the motion. How many revolutions will the wheel make before coming to rest?

    2. Relevant equations

    3. The attempt at a solution
    I'm lost at how to start this problem, I tried to get the deceleration caused by the 9N force applied on the wheel by Newton's Second Law but I couldn't get the mass, so i used the I=M*R2 equation to get the mass and then used F=M*a to find the deceleration, took that answer and divided by 2pi to find the revolutions, but the answer was off. What am I missing?
  2. jcsd
  3. May 9, 2009 #2


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    Homework Helper

    The angular deceleration is given by [itex]a= \alpha r[/itex]. Find [itex]\alpha[/itex]. Then use the equations of rotational motion to find the total angular displacement from the initial angular velocity to rest.
  4. May 9, 2009 #3
    I used a=alpha*r and i got the alpha to be .003, using Omegaf2=Omegai2+2*alpha*Theta i get 28166, but the answer should be 672.9

    EDIT: nevermind, i got it, thanks!
    Last edited: May 9, 2009
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