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Homework Help: Physics question dynamics?

  1. Apr 13, 2012 #1
    1. The problem statement, all variables and given/known data

    The constant force that works in the object M=5 kg forces the object with mass m=4 kg to move with acceleration a=2 m/s^2.
    The coefficient of friction between M and the table is 0.2.
    Determine
    a)F=? b) T=?

    2. Relevant equations


    3. The attempt at a solution
    SOLUTION:
    F-Ff=(m)*a Here I find F
    and here I find F
    B) F-(T+Ff)=m*a or T=m2*g ;G-T=m*g

    Picture to help you http://i1171.photobucket.com/albums/r549/Elaia06/jh.jpg [Broken]

    Edited: Maybe it is F-Ff=(m+M)*a where Ff =M*g*0.2?
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Apr 13, 2012 #2

    PhanthomJay

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    Draw a free body diagram of each mass separately (one for m and one for M). For the mass on the table, there is another force besides F and F-f acting in the x direction. For the hanging mass there are 2 forces acting. Use Newton 2 for each and solve the 2 equations for the 2 unknowns.
     
  4. Apr 13, 2012 #3
    I know,its also the tension but I wanna know if my equations are written in the right way?
     
  5. Apr 13, 2012 #4

    PhanthomJay

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    They are not. First distinguish between m and M. Write your force equations for each block.
     
  6. Apr 13, 2012 #5
    I edited it
     
  7. Apr 13, 2012 #6

    PhanthomJay

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    Do not solve it this way. You will be headed for trouble. Look at each block separately please.
     
    Last edited: Apr 13, 2012
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