How Does the Leftmost Block Affect the Middle Block in a Force Chain?

[darklich21]

Homework Statement

Blocks of 1.0, 2.0, and 3.0 kg blocks are lined up on a table (1kg block being on the left, 2kg in the middle, 3kg being on the right). A rightward poiting 12 N force is applied to the leftmost block. What force does the leftmost block exert on the middle one?

Homework Equations

F=ma
a= Force applied / (m1 + m2 +m3)
a= 12N/6k= 2m/s^2

The Attempt at a Solution

Ok so this is what I did:

12N + F(1on2)=(mass of 2nd block)(acceleration)
12+F(1on2)=(2kg)(2m/s^2)
F(1on2)=8N, I got this wrong. Did i miss something, or should this force actually be negative.

 

[kuruman]

You got he acceleration right and that is good.

The 1 kg block exerts a force on the middle block that is to the right. The 3 kg block exerts a force on the the 2 kg block that is to the left. You don't have that one. Added together these forces are the net force on the 2 kg block.