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Homework Help: Pulley Tension friction help?

  1. Dec 18, 2011 #1
    Pulley Tension friction help??

    1. The problem statement, all variables and given/known data

    6533043261_33117fa1e7.jpg
    http://www.flickr.com/photos/72384417@N06/6533043261/ [Broken] by LiFK1, on Flickr

    Mass1 = 0.750 kg
    Mass2 = 0.52 kg
    Fk=2.1 N
    g= 9.8 N


    2. Relevant equations

    F=ma
    Mass1(gravity)= (Mass1+mass2)Acceleration
    T + m2g - fk = (m1 + m2)a

    3. The attempt at a solution
    Mass1(gravity)= (Mass1+mass2)Acceleration
    7.35=(0.750kg+0.52kg)A
    5.787 N = A

    T + m2g - fk = (m1 + m2)a
    T + 0.52kg(9.8)-2.1=1.27(5.78)
    T = 4.35 N
    rounded up T = 4.4N

    Apparently the answer to this is 4.2 N, but i cant seem to get it.
    Can someone tell me what im doing wrong?
    thanks in advance.
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Dec 18, 2011 #2
    Re: Pulley Tension friction help??

    You should draw a diagram showing the forces acting on each object.
    The weight has 2 forces it's weight = 0.75 x 9.81 and the tension in the string
    The cart has 2 forces the tension in the string and friction.
    If you look at these 2 situations you should get 2 equations that enable you to calculate the acceleration and the Tension in the string.
    Hope this helps.
     
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