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physics problem: normal force

 
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Sep16-04, 07:07 PM   #1
 

physics problem: normal force


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?
 
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Sep16-04, 07:30 PM   #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.
 
Sep16-04, 07:56 PM   #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]
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Sep16-04, 08:49 PM   #4
 

physics problem: normal force


Thank you very much guys. Leong, the picture really helps.
Thanks again.
 
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