Finding Force of Contact: 2kg and 3kg Blocks with 10N Horizontal Force

[aishax]

A 2-kg block A and a 3-kg block B are in contact on a frictionless table. A horizontal force of 10N is applied to A. Find the force with which B resists the pressure of A.

The answer is -6N. I realize this is a very simple question, I would just like to understand how to get the solution. Thanks in advance :)

 

[mezarashi]

Hi aishax, welcome to PF.

Start with drawing some free-body diagrams:
- One of the complete system (A + B)
- One of A only
- One of B only
Hint: The force felt by B must be the amount that makes it accelerate at the same rate as A and as A+B.

What are the "external forces" in each case?

 

[aishax]

Hello mezarashi :)

Alright, I drew each of those FBDs. I found the acceleration of the system, which was 2.0 m/s^2. I used the acceleration, and found the Fapp on mass A, which was 4.0 N. And Fapp for mass B is 6.0 N.

The external forces are Force normal, and force applied. I'm still a tad lost on the concept still, unfortunately.