1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Pulley System- equation derivation

  1. May 26, 2010 #1
    1. The problem statement, all variables and given/known data

    Determine a formula for acceleration of the system shown in Fig. 4-45 if the cord has a non-negligible mass mc. Specify in terms of lA and lB, the length of cord from the respective masses to the pulley ( The total cord length is l= lA + lB)

    [PLAIN]http://img706.imageshack.us/img706/8575/3333v.png [Broken]

    2. Relevant equations

    F = ma

    3. The attempt at a solution

    Fby = Fax

    Fby = mB *g

    acceleration of system: a = (mB *g)/ma

    acceleration of system with non-negligible cord

    a = (mB + (mC * (lB/ l)))*g / (ma + (mC * (lA/ l)))

    need an answer check, I can't tell if its right.
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. May 27, 2010 #2


    User Avatar
    Homework Helper

    This is not right. Draw the free-body diagram, showing the forces both at A and B.
  4. May 27, 2010 #3
    Is my whole solution wrong, or just the forces I used.

    I understand now that I didn't use tension force, but is the way I derived the equation wrong with

    Fby = Fax
  5. May 27, 2010 #4


    User Avatar
    Homework Helper

    If you do not specify what Fbx and Fax are the equation Fbx=Fax has no sense.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook