Find force and coefficient of friction between 2 stacked blocks in motion

[gabemarkus]

Homework Statement

The surfaces of two blocks are roughened so that they do not slide against each other when a force of 30N is applied to the bottom block. 1.Find the force of friction between the two blocks. 2. Find the minimum coefficient of friction needed between the two blocks so that the top block does not move.

Homework Equations

Fnet = ma
muK = Fk/Fn
mu s = Fs,max/Fn

The Attempt at a Solution

I found the acceleration of the two block system, which is 2 m/s². I'm wondering if you have to find the Fn of the 5kg block then act as if it was moving 2m/s² by itself over the 10kg block then determine Fk from that and plug it into muK = Fk/Fn. Thanks for any help!

 

[gabemarkus]

Or, do you have to find the accelerations of the blocks separately at first?

 

[haruspex]

Homework Statement

View attachment 73930
The surfaces of two blocks are roughened so that they do not slide against each other when a force of 30N is applied to the bottom block. 1.Find the force of friction between the two blocks. 2. Find the minimum coefficient of friction needed between the two blocks so that the top block does not move.

Homework Equations

Fnet = ma
muK = Fk/Fn
mu s = Fs,max/Fn

The Attempt at a Solution

I found the acceleration of the two block system, which is 2 m/s². I'm wondering if you have to find the Fn of the 5kg block then act as if it was moving 2m/s² by itself over the 10kg block then determine Fk from that and plug it into muK = Fk/Fn. Thanks for any help!

Finding the acceleration of the system was the right first step. (I assume there's no friction between the lower block and the ground.) I'm not sure what you are suggesting as the next step. Why not apply it and post the working that results? That will be a lot clearer.