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Homework Help: Want to verify textbook ans on angular velocity

  1. Nov 13, 2005 #1
    I got the following qn:

    In a circus performance, a large 5kg hoop of radius 3m rolls without slipping. If the hoop is given an angular speed of 3 rad/s while rolling on the horizontal and allowed to roll up a ramp inclined at 20 degrees with the horizontal, how far(measured along the incline) does the hoop roll?

    My solution is as follows:
    Total initial energy=0.5 * I * (angular velocity)^2
    =0.5 * 45 * 3^2
    =202.5
    Final energy = mgh
    = 5gh, where h is the vertical height
    Equating the 2,
    202.5=5gh
    h=4.128.

    Since we want to find the distance along the slope, d, d=h/sin20 = 12.1m

    This is the ans I got, but it seems that the back of the textbook ans is 24m . Is the textbook ans correct or wrong?
     
  2. jcsd
  3. Nov 13, 2005 #2

    Physics Monkey

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    You included the rotational kinetic energy but forgot the translational kinetic energy.
     
  4. Nov 13, 2005 #3
    Thanks! How could i have forgotten that?
     
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