What Force Does Block B Exert on Block A?

[Thegiver431]

Homework Statement

A hand pushes on block A. Block B is on the right side of block A. If block a has A mass of 20kg and block B has a mass of 12 kg, and the acceleration equals 4m/s^s, what is the force that block B exerts on Block A [/B]

Homework Equations

F=m/a
[/B]

The Attempt at a Solution

F=20kg/4m/s^2 but I am not sure if this, in which I used the mass for block A, is it or if i have to use block B mass. I am kind of confused on which one

 

[Nathanael]

The force that block B exerts on block A is the same as the force that block A exerts on block B (that's one of Newton's laws).

You could find this force by evaluating the forces for either block A or block B, but it would be easier to analyze block B.

What are all the forces acting on block B? What is the net force on block B? (F_{net}=ma)