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Homework Help: Three blocks on a fricionless horizontal surface

  1. Sep 24, 2004 #1
    OK, three blocks on a fricionless horizontal surface are in contact on each other, a force is applied to block 1, m1, m2, m3, respectively. And m1=m2=m3.

    how come the force of contact that block one exerts on block is F(m2+m3) / (m1+m2+m3) instead of just F*m2/(m1+m2+m3). ( I know that a is F/(m1+m2+m3).)
     
  2. jcsd
  3. Sep 24, 2004 #2

    Pyrrhus

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    Think about Action and Reaction Forces [Contact Forces] acting on each block.
     
  4. Sep 24, 2004 #3
    Right direction : Positive; Left direction: Negative.
    [tex]
    \begin{multline*}
    \begin{split}
    &Newton's\ 2nd\ Law:\\
    &\sum \vec{F}=m\vec{a}\\
    &Consider\ m_1:\\
    &F+(-Fm_1m_2)=m_1a\\
    &F=m_1a+(Fm_1m_2)\ .........(1)\\
    &Consider\ m_2:\\
    &Fm_2m_1+(-Fm_2m_3)=m_2a\ .....(2)\\
    &Consider\ m_3:\\
    &Fm_3m_2=m_3a\ .....(3)\\
    &(3)\rightarrow(2):\\
    &Fm_2m_1=m_2a+m_3a\ .....(4)\\
    &(4)\rightarrow(1):\\
    &F=m_1a+m_2a+m_3a\ .....(5)\\
    &From\ (4):\\
    &Fm_2m_1=(m_2+m_3)a\\
    &=\frac{F(m_2+m_3)}{m_1+m_2+m_3}\\
    \end{split}
    \end{multline*}
    [/tex]
     

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