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Rotations from angular acceleration and final angular velocity

  1. Nov 14, 2016 #1
    1. The problem statement, all variables and given/known data
    At a fair, Hank and Finn play with a horizontal 5.4 m long bar able to rotate about a pole going through its exact center. Hank pushes with 32 N at one end of the bar and Finn pushes with 18 N in the opposite direction at the other end. (Assume both forces are always perpendicular to the bar.) The bar rotates from rest with a constant angular acceleration of 0.35 rad/s^2.

    Hank and Finn were able to spin the bar up to an angular speed of 3.1 rad/s. How many turns around the pole did they make to push the bar?

    2. Relevant equations
    w^2=wi^2+2(alpha)theta

    3. The attempt at a solution
    (3.1)^2=0+(2(.35)theta
    theta =13.7
    theta/2pi=#of rotations
    =2.18 rotations

    I don't have the correct answer for this so I have no idea if I'm doing this correct or not.
     
  2. jcsd
  3. Nov 14, 2016 #2

    gneill

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    Staff: Mentor

    Your method and result are fine.

    Please don't make pleas for help in your thread titles. The question didn't really involve torque calculations, did it? I'll change the title to something appropriate.
     
  4. Nov 14, 2016 #3
    Sorry about that, and there are two forces acting on it, but you find the mass later by doing the sum of the torques=I*alpha
    That wouldn't apply to this would it?
     
  5. Nov 14, 2016 #4

    gneill

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    Staff: Mentor

    It would apply to a question where it asks you to find the mass, but that wasn't the question asked this time.
     
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