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Homework Help: Dynamics Pushing Blocks

  1. May 21, 2014 #1
    Please look at pictures.
    Weirdly, my textbook does not give the answer to this question.

    Can you check my answer? Sorry for the really bad writing. If you ask, I can more clearly write it.

    Attached Files:

    Last edited: May 21, 2014
  2. jcsd
  3. May 21, 2014 #2


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    The handwriting is decipherable, but it's hard to follow what you are doing because it's not clear which equations relate to which FBD.
    Please post your working by typing - it's not hard - making it clear which forces relate to which body.
    Click on the Go Advanced button. You can pick ∑ off the quick symbols on the right and superscript and subscript from the X2, X2 icons along the top.
  4. May 21, 2014 #3
    Here goes nothing!
    For m1:

    For m2:

    Add both ∑Fx equations:

    a=1.41 m/s^2

    That looks great! How about the physics?
  5. May 21, 2014 #4


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    You've missed something out. Write out the equations relating N1, F, fk.
  6. May 21, 2014 #5
    I do not understand. Can you be more specific? What is it I am missing? I've been looking at the problem long enough that everything seems good.
  7. May 21, 2014 #6
    Got it. I mixed up the fk equation. I'm fixing it now and posting the new solution.
  8. May 21, 2014 #7

    Here is my new equation:


    a=1.16 m/s^2
    N12=N21=10.52 N
  9. May 21, 2014 #8


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    Those answers are correct (and if they're not, we made the same mistakes hahah)

    Except for the rounding, if you rounded a to 2 decimals it would actually go up to 1.17 but that's pedantic, your equation is correct.

    edit: Actually, there should be a negative sign in very the beginning of your first equation, but you must have just forgotten to type that, because your answer is correct.
  10. May 21, 2014 #9
    Yes, I did forget the minus! I hope someone else confirms! At least we are two ;)
  11. May 22, 2014 #10


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    Make that three.
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