[Physics] [homework] The static friction coefficient (μs)

[Caplockfury]

Hello!
_______(B)__(A)
------->[3kg][2kg]
60n____0 0


Object B is being pushed by 60 newtons of force. I need to find the static friction coefficient (μs) between A and B so that A doesn't fall. (the 0's are wheels) (The answer is 0.817)

I'm not really sure how to tackle this. G(A) is 19.6n. I'm sorry I couldn't include more work but I'm french and I'm not sure of many of the terms to use :\

[TestTubeGames]

Well, it seems you've figured out the force of gravity on A. In order for A not to fall, static friction has to balance it out. Hrm, so how do we figure out how much static friction is there?

I'd say your next step is to find the equation for the force of friction. Once you have that, you've almost got the problem solved...

[yurell]

I'm sorry, I really can't tell what's going on from your diagram. Is there any chance you could explain it in words (or, failing that, upload a better diagram)?

[Seraph]

Draw the free body diagram for object A, and then solve for the forces.

There are three forces.
1) The force of gravity on object A. (you have this)
2) The force of block 'B' pushing block 'A' to the right. (use F=ma a few times)
3) The force of friction between block 'B' and block 'A'. (I assume you know how to do this once you solve for force 2)

[yurell]

You may find it easier to rotate the problem: have A sitting on the plane of block B, with gravity pushing as a force to the right. I had a similar problem with a train in first year, and I found it much more intuitive that way.

[eSOANEM]

I tend to prefer solving these problems in the accelerating frame (I know, I know). In this case, you can, without too much trouble, reduce it to a block on a slope problem.