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Homework Help: Contact Force with two masses given

  1. Jun 18, 2016 #1
    1. The problem statement, all variables and given/known data
    A 3.0 kg and a 5.0 kg box rest side by side on a smooth, level floor. A horizontal force of 32 N is applied to the 3.0 kg box pushing it against the 5.0 kg box, and, as a result, both boxes slide along the floor. How large is the contact force between the two boxes?

    a) 32N b)24N c) 0N d)20N e) 12N

    2. Relevant equations

    3. The attempt at a solution
    I found the total mass which is 8kg. And then using the F=ma equation, I found my acceleration which is 4 m/s^2. And now...I'm completely stuck on what to do. In class we weren't given an example like this, so I don't know where to go from here...
  2. jcsd
  3. Jun 18, 2016 #2


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    Staff: Mentor

    Can you show us your free body diagram (FBD) for each of the two boxes? :smile:
    Last edited: Jun 18, 2016
  4. Jun 18, 2016 #3


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    2017 Award

    Staff: Mentor

    You know mass and acceleration of the 5 kg block.

    But I'm not sure if the blocks are really supposed to be frictionless. The answer does not depend on that question, but the points you get for the answer could if there are points for intermediate steps.
  5. Jun 18, 2016 #4
    Yes lol I do but there's no way for me to upload my image from my smartphone since my laptop won't allow me to connect it anymore. Basically I cant upload an image, but I did draw a free body diagram, with two boxes sitting on a horizontal line with the force of 32N being pushed to the right (----->) like this, upon the 3.0kg box. Dunno if that really....explains it, but that's what I drew...
  6. Jun 18, 2016 #5
    I finally figured it out! F_2 = m_2 x acceleration. Therefore I get 20 as my answer! Iol I at least appreciate the time you guys used to reply to my question. Many thanks.
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