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Homework Help: 2 boxes with 1 applied force

  1. Sep 11, 2008 #1
    1. The problem statement, all variables and given/known data
    Box A
    Mass=3.2kg
    Force of Friction=2 Newtons

    Box B
    Mass=2.1kg
    Force of Friction=1 Newton

    Force applied 10.5 Newtons [horizontally].

    http://img162.imageshack.us/img162/7697/f1qd1.png [Broken]

    Q. Find the magnitude of the force of contact between the two boxes.

    2. Relevant equations
    F=ma


    3. The attempt at a solution

    I need to find acceleration first since the Force of Friction of both boxes is not greater than the Force Applied.

    Fnet=(mA+mB)a

    (mA+mB)a=Fa-(FfA+FfB)
    (3.2kg+2.1kg)a=10.5N-(2N+1N)
    (5.3kg)a=10.5N-(3N)
    a=10.5N-(3N)/5.3kg
    a=7.5N/5.3kg
    a=1.415m/s/s

    Now, I tired many, many methods of solving for this from here on, including the example from this page:https://www.physicsforums.com/showthread.php?t=202002

    However, the result seems still to be wrong.
    I got 7.5N as the internal force both boxes act upon eachother.

    Any help is appreciated although not dire.
     
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Sep 12, 2008 #2

    alphysicist

    User Avatar
    Homework Helper

    Hi fahlim003,

    I'm not getting the answer of 7.5N. Can you show how you got it?
     
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