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Homework Help: Tension between 2 blocks and friction.

  1. Sep 21, 2008 #1
    1. The problem statement, all variables and given/known data


    A block of mass m1 = 2 kg and a block of mass m2 = 3 kg are tied together and are pulled from rest across the floor by a force of P = 25 N. The coefficient of friction of the blocks with the floor is µ = 0.14.

    I found the acceleration to be 3.6266 m/s2.

    I need to find the tension in the string between the blocks.

    2. Relevant equations

    F=ma and Ff=u(mg)

    3. The attempt at a solution

    The total frictional force is 6.867 N. m1 has a frictional force of 2.7468 i think, and m2 has a frictional force of 6.7596 i think. I think the pulling force on m1 is 7.2532 N. I mean, i tried creating different summations of the forces, but I don't know what I'm doing wrong. I'm sure I could figure it out, but I need to at least know how to add the forces up in each direction. Thanks so much.
  2. jcsd
  3. Sep 22, 2008 #2


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    Good. You should round it off though to 3.6

    where did you get this?
    how did you arrive at this?
    Draw a Free Body Diagram of block 1 (isolate it) , and examine the forces acting on it to solve for T using Newton 2. What is the acceleration of block 1?
  4. Sep 22, 2008 #3
    okay, I typed the wrong number in for m2's frictional force. I meant to type in 4.1202 N. I arrived at m1's pulling force by (2)(3.6) = F. Right, I thought I tried creating a FBD but for some reason I'm doing something wrong. Is the acceleration on block m1 = 2.25 m/s2? At this point I am not sure what I am supposed to do.

    EDIT: wait, doesn't the acceleration have to be equal to 3.6m/s2?
    Last edited: Sep 22, 2008
  5. Sep 22, 2008 #4
    Hey, if someone could help me. I'm really stuck on this one, I just think I've dug myself a deeper hole trying to work this out. I would really appreciate any more help.

    EDIT: I solved it. it's 10 N...
    Last edited: Sep 23, 2008
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