physics problem: normal force

lmf22

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?

recon

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.

Leong

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 Thumbnails

 

lmf22

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