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Two blocks touching on a table, one with friction and the other w/out

  1. Feb 27, 2013 #1
    1. Two blocks, of masses M = 3 kg and m = 2 kg, are in contact on a horizontal table. A constant horizontal force of magnitude F = 5 N is applied to block M as shown. There is a constant frictional force of magnitude f = 1 N between the table and the block m, but no frictional force between the table and the first block M.

    (a) calculate the acceleration of the two blocks
    (b) calculate the force of contact between the blocks.




    2. F=ma
    F=[itex]\mu[/itex]N




    3. Usually these problems are no problem for me; however, this one is confusing me tremendously since there is only friction on one block and not the other. I'm just not sure how it affects the answers to the questions being asked.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Feb 27, 2013 #2
    Re: Two blocks touching on a table, one with friction and the other w/

    Hi codytanner16

    Have you drawn your free-body diagrams for both blocks?
     
  4. Feb 27, 2013 #3
    Re: Two blocks touching on a table, one with friction and the other w/

    I have tried, but I think that maybe where I need some help. I'm not sure which force come into play for which blocks.
     
  5. Feb 27, 2013 #4
    Re: Two blocks touching on a table, one with friction and the other w/

    What forces have you already drawn in for the blocks?
     
  6. Feb 27, 2013 #5
    Re: Two blocks touching on a table, one with friction and the other w/

    1. The force down due to gravity for the larger block.
    2. The force to the right, from the pushing force, for each block.
    3. The force due to friction down for the smaller block.

    Am i close?
     
  7. Feb 27, 2013 #6
    Re: Two blocks touching on a table, one with friction and the other w/

    Since the blocks are making contact with each other, then each block will exert a force on the other one ( these are action-reaction forces ).
    Also, for (2) the force to the right on each block may be different.

    Also, remember the normal forces.
     
  8. Feb 27, 2013 #7
    Re: Two blocks touching on a table, one with friction and the other w/

    For the first part of the question, since the 2 blocks move together, then you can consider them to comprise one object.
     
  9. Feb 27, 2013 #8
    Re: Two blocks touching on a table, one with friction and the other w/

    Thanks!

    How does the fact that there is only friction on one block and not the other affect the acceleration of the two blocks?
     
  10. Feb 27, 2013 #9
    Re: Two blocks touching on a table, one with friction and the other w/

    If you're taking the 2 blocks as one object, then that's the total friction on the object.
     
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