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Homework Help: Physics problem: normal force

  1. Sep 16, 2004 #1
    A 38.0 kg box (m1) rests on a table. A 17.0 kg box (m2) is placed on top of the 38.0 kg box. What is the normal force that the 38.0 kg box exerts on the 17.0 kg box.

    I found that the normal force of just the 38.0kg box is 372.78N and the normal force of just the 17.0kg box is 166.77N. But I don't know how to figure out the normal force that the 38.0kg box exerts on the 17.0kg box.

    any help?
     
  2. jcsd
  3. Sep 16, 2004 #2
    The 17.0 kg box exerts a force of 166.77 N on the 38.0 kg box. Therefore, the normal force is _______. <--- figure it out yourself.
     
  4. Sep 16, 2004 #3
    Upward direction : positive; downward direction : negative
    [tex]\begin{array}{cc}\\
    Consider\ mass\ m_1:\\
    Newton's \ 2nd\ Law\\
    \sum \vec{F} =m\vec{a}= 0 \ in\ this\ case\\
    Fm_2m_1+(-m_2g)=0\\
    Fm_2m_1 = m_2g\\
    = 17.0*9.81\\
    = 168 \ N\\
    Fm_2m_1= - Fm_1m_2 : Newton's \ 3rd\ Law\\
    \end{array} [/tex]
     

    Attached Files:

  5. Sep 16, 2004 #4
    Thank you very much guys. Leong, the picture really helps.
    Thanks again.
     
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