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Homework Help: Laws of Motion Problem

  1. Jan 10, 2014 #1
    1. The problem statement, all variables and given/known data

    Two blocks of mass m1 and m2 (m2 = 2 kg ; m1 = 3 kg)are connected with a spring moving on smooth plane. The acceleration of block of mass m2 is 2 ms-2, find acceleration of block with mass of 3kg.


    2. The attempt at a solution

    Let external force of F be applied on Block m2.
    ∴ By only considering m2, we get
    F - T = 6
    and for block m1
    T = 2a
    and by newton's law of system (Fnet = m1a1+m2a2+m3a3+........)
    F = 6 + 2a
    But by solving these three equations, i am not getting the answer.
    Plz help...........

    Attached Files:

  2. jcsd
  3. Jan 10, 2014 #2


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    hi rajumahtora! :smile:

    (i don't really understand the question, there seems to be something missing, but anyway …)
    shouldn't that be 3a ? :wink:
  4. Jan 10, 2014 #3


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    There's no mention of an external force in the OP.
    I think you're getting your m1 and m2 mixed up. m2 needs a net force of 4N.
    Having considered the two masses separately, you are not going to get any additional equations by considering the whole system. If you correct your errors you will find that the whole system equation can be deduced from the other two. In fact, if there is an unknown external force, you do not have enough information to answer the question.
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