1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Required tangential force to move spool

  1. Dec 2, 2014 #1
    This should be an easy one, but my answer does not seem right to me. I was hoping someone to verify for me.

    If you have a spool filled with rope that weighs 2,000 LBS on a frictionless axle. Determine the tangential force required to move the spool by pulling the rope.

    Given:
    Weight of spool = 907.18 KG
    Diameter of spool = 1.22 Meters
    Angular Acceleration = 2.093 RADs per Second
    Length of spool = .74 Meters
    T = Torque
    A = Angular Acceleration
    R = Radius of spool in meters

    Explanation of calculations:

    I calculated the moment of inertia for the full spool and used it to derive the torque (knowing the angular acceleration) and then derived force out of the torque equation.

    Calculations:

    I = 1/2*M*(L squared)
    I = .5*907.18*.547
    I = 248.11 KG*(Meters squared) Moment of inertia in Kg*Meters - squared

    If I = T/A then

    248.11*2.093 = T
    T = 519.29 Newtons*Meters

    If T = F*R then


    519.29 / .61 = F
    F = 851.29 Newtons

    As far as my tension in rope I assume it to be equal to F at 851.29 Newtons Is this correct? The value seems high to me. Please advise.


     
  2. jcsd
  3. Dec 2, 2014 #2

    CWatters

    User Avatar
    Science Advisor
    Homework Helper

    I haven't checked your working but...

    851 Newtons is about the same force that an 85kg man exerts on the ground due to gravity. That doesn't seem like a lot given your 2000lb spool accelerates at 2 rad/s/s. (about 114 deg/s/s)
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted