Prelim Physics help please (2 Viewers)

[Zeyi]

A warehouse worker applies a force of 420N to push 2 crates across the floor as shown in the attached diagram.

The friction force opposing the motion of the crates is a constant 2N for each kilogram.
What is the force exerted on the 30kg crate by the 40kg crate?

 

[trea99]

The crates are moving together so they have the same acceleration;
Net force on 70kg system = 420 - 2(70) (2N per kilogram for 70kg moving together)
Net force on 70kg system = 280N
Acceleration of 70kg system = 280/70 = 4ms^-2
Both the 30kg and 40kg crates have an acceleration of 4ms^-2 (to the right or whichever direction they are being pushed)
The force on the 30kg crate by the 40kg one is equal to the force on the 40kg crate by the 30kg crate (Newton's Third Law)
F = ma
F = (40)(4)
F = 160N (in whatever direction)
This is the force the 30kg crate exerts on the 40kg crate which is the same as the force the 40kg crate exerts on the 30kg one but in the opposite direction.
Correct me if I'm wrong but I think the answer is 160N (to the left according to the diagram)