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Rotational Kinetic Energy

  1. Apr 3, 2012 #1
    1. The problem statement, all variables and given/known data

    You attach a mass M to a string and wind the string around the circumference of a wheel. The wheel has two hubs with radii R1 and R2 with R2 > R1. You perform two experiments. First you wind the string around the smaller radius wheel and allow the mass to fall a distance h. In the second experiment you wind the string around the larger radius wheel and allow the mass to fall a distance h. Rank the rotational kinetic energy Krot of the wheel for each experiment.


    2. Relevant equations

    1/2I(ω^2)

    3. The attempt at a solution

    Basically I was thinking that ω is independent of the radius so they would be equal
    but then if I=m(r^2) and ω = v/r then
    I(ω^2)=1/2m(r^2)(v^2/r^2) and the r's cancel out giving us rotational kinetic energy = 1/2mv
    So would the rotational kinetic energies be equal or would 1 be larger than the other?
     
  2. jcsd
  3. Apr 3, 2012 #2

    gneill

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    Staff: Mentor

    Think about energy conservation. Where does the energy come from to turn the wheel?
     
  4. Apr 3, 2012 #3
    Wouldn't it have came from the potential energy mgh?
     
  5. Apr 3, 2012 #4

    gneill

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    Staff: Mentor

    Is that a guess? :devil:
     
  6. Apr 3, 2012 #5
    haha alright, I think I got it, thanks
     
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