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!

Mastering Physics: Acceleration of a Pulley

  1. Apr 15, 2017 #1
    1. The problem statement, all variables and given/known data
    A string is wrapped around a uniform solid cylinder of radius r, as shown in (Figure 1) . The cylinder can rotate freely about its axis. The loose end of the string is attached to a block. The block and cylinder each have mass m.
    Find the magnitude α of the angular acceleration of the cylinder as the block descends.
    upload_2017-4-15_19-12-53.png

    2. Relevant equations
    F=ma=mg-T
    Torque=Iα=-Tr
    a=-rα
    I=mr2/2
    3. The attempt at a solution
    I use these three equations to eliminate T and solve for α.

    m(-rα)=mg-T
    -1/2mr=T
    -mrα=mg+1/2mr
    -α=g/r+1/2
    α=-1/2-g/r

    I tried this answer however it was wrong.

    Mastering says the correct answer is
    α = 2g/3r

    I'm really not sure where this comes from, so any help would be great! I need to understand where I went wrong.
     
  2. jcsd
  3. Apr 15, 2017 #2
    Where did this come from? It doesn't look right.

    Edit: Okay, now I see what you did. You were equating Iα to -Tr, then substituting I = mr2/2 for I. You should work through that algebra again and I think you'll find your problem.
     
  4. Apr 15, 2017 #3
    I dropped the g. Thank you so much! I found the correct answer.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Mastering Physics: Acceleration of a Pulley
Loading...