Maximum Static Force before Blocks Slip

[patchums]

An 6.40kg block rests on a 12.5kg block. The interface between the lower mass and the table is frictionless, but there is friction (static friction μs and kinetic friction μk) between the two blocks. A horizontal force F acts on the upper block and causes both blocks to accelerate. The acceleration of both blocks when they begin to slip is 2.0 m/s2.

fk=μkFN
fs=μsFN

I guess I have no idea how to start with this question. Am I supposed to find the normal force first and work from there? Where do I even go from there? Any help would be appreciated, thanks much!

 

[gneill]

An 6.40kg block rests on a 12.5kg block. The interface between the lower mass and the table is frictionless, but there is friction (static friction μs and kinetic friction μk) between the two blocks. A horizontal force F acts on the upper block and causes both blocks to accelerate. The acceleration of both blocks when they begin to slip is 2.0 m/s2.

fk=μkFN
fs=μsFN

I guess I have no idea how to start with this question. Am I supposed to find the normal force first and work from there? Where do I even go from there? Any help would be appreciated, thanks much!

You haven't stated what it is you're trying to find...

 

[patchums]

Aw geez, sorry. I have to find the force at the time when the blocks start to slip.

 

[gneill]

Aw geez, sorry. I have to find the force at the time when the blocks start to slip.

Okay, so immediately before the blocks begin to slip they are essentially one large block...

 

[vivekrai]

Try to imagine by sitting on the lower block. What you see? Where should the force act?