Contact force between boxes when 9 N pushes three boxes

[BugsSport]

Homework Statement

A force of magnitude 9.00 N pushes three boxes with masses m1 = 1.30 kg, m2 = 2.80 kg, and m3 = 4.90 kg

Find the magnitude of the contact force between boxes 1 and 2.

Homework Equations

Fnet,x = ma?

The Attempt at a Solution

I thought that it would be 9.00 N, since the boxes are back-to-back-to-back, but that answer is wrong.

 

[LowlyPion]

Homework Statement

A force of magnitude 9.00 N pushes three boxes with masses m1 = 1.30 kg, m2 = 2.80 kg, and m3 = 4.90 kg

Find the magnitude of the contact force between boxes 1 and 2.

Homework Equations

Fnet,x = ma?

The Attempt at a Solution

I thought that it would be 9.00 N, since the boxes are back-to-back-to-back, but that answer is wrong.

Welcome to PF.

At the interface between 1 and 2, the mass of 2 and 3 has already been accounted for by the force, so the force required to accelerate the remaining mass is given by the force that it needs to still push.

Otherwise, if that force was still the whole 9N, then applying that to the total mass left would result in an acceleration to the left that just wouldn't be there.

 

[BugsSport]

okay got it thank you