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Cylindrical fishing reel problem using moment of inertia

  1. May 4, 2009 #1
    1. The problem statement, all variables and given/known data
    A cylindrical fishing reel has a mass of 0.85 kg and a radius of 4.5 cm. A friction clutch in the reel exerts a restraining torque of 1.6 N·m if a fish pulls on the line. The fisherman gets a bite, and the reel begins to spin with an angular acceleration of 66 rad/s2.
    a) Find the force of the fish on the line.
    b) Find the amount of line that unwinds in .5 seconds.


    2. Relevant equations
    I = .5mr^2
    theta = .5at^2


    3. The attempt at a solution
    I found the moment of inertia to be 8.606. What I don't understand is how to relate the torque to the moment of inertia. I dont know if my calculator should be set to radians or degrees, but I tried both ways and got them both wrong.
     
  2. jcsd
  3. May 4, 2009 #2

    LowlyPion

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    First of all I needs to be calculated with the radius as .045. That makes your I off by a factor of 104

    I = 8.6*10-4

    T = a*I

    So accounting for the force on the line and the restraining force ...

    F*.045 = 1.6 + 66*8.6*10-4

    You have the right equation for b. Just remember that since θ is in radians, you need to provide θ*r for the length of line that reels off.
     
  4. May 4, 2009 #3

    LowlyPion

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  5. May 26, 2009 #4
    Alright thanks so much! I understand how to do it now!
     
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