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Force applied to 2 connected mass.

  1. Mar 29, 2014 #1
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    A force is applied to m1 connected to m2 by a "massless" cord. where m2>m1.

    the acceleration, a, is a = F/m1+m2

    By decomposing the system into A and B where A refers to the tension on m1 upon having the force applied onto m2, the tension TA is to the positive x-direction.

    However, in the case of the system B, the tension TB is to the negative x-direction as the force F is applied directly to m2.

    Why does TB arises in the block m2 but yet not in m1?
     
  2. jcsd
  3. Mar 29, 2014 #2

    Doc Al

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    I'm not sure I understand this statement. The cord connecting the two masses exerts a tension force on both m1 and m2. The cord exerts the same force on both blocks (different directions, of course).
     
  4. Mar 29, 2014 #3
    I shall rephrase. I was lacking clarity in the OP.

    When force F is applied on m2, m1 experiences a tension TA in the positive x-direction. (why shouldn't m1 experience another tension in the negative x-direction. By my understanding, there should be an equal and opposite reaction.

    In the case of m2, upon the appliance of the force F, the m2 experience not only the force F in the positive x-direction but also a tension TB in the negative x-direction.
     
  5. Mar 29, 2014 #4

    Doc Al

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    Right. Tension is created in the cord, which acts on both masses.

    What would create that tension?

    A reaction from what?

    And if the mass m1 were connected to a third mass, then it too would experience a tension force acting to the left. But there is no third mass.

    (Note that the force F and the tension in the cord are not equal.)
     
  6. Mar 29, 2014 #5

    A reaction from m1 having experience a force F applied to m2?

    Suppose, as you've suggested that a third mass m3 was attached to m1 to the left. If the same force F were applied, then aside from m2 having experienced the tension TB, m1 would now experience a tension in the negative x-direction, am I right?
     
  7. Mar 29, 2014 #6

    Doc Al

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    I'm not sure what you mean by a 'reaction'. m2 pulls on m1 (via the massless cord) and m1 pulls back on m2.

    Sure. The force F will end up creating various tensions in the cords connecting the masses.
     
  8. Mar 29, 2014 #7
    Yes there is a reaction (Newton's 3rd law). What made you believe there isn't one?
     
  9. Mar 29, 2014 #8
    Come on, Doc. he's talking about Newton's 3rd law. quoting from your post " m2 pulls on m1" - That's the action - "and m1 pulls back on m2" - That's the reaction.
     
  10. Mar 29, 2014 #9

    I understand there to be one but it isnt outlined by my lecturer.
     
  11. Mar 29, 2014 #10

    Doc Al

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    That's why I used it as an example. But I don't think that's what was meant. (I think he was looking for a second force acting on the trailing block.)
     
    Last edited: Mar 29, 2014
  12. Mar 29, 2014 #11
    That doesn't mean it's not there.
     
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