How Do You Determine When to Use Static vs Kinetic Friction in Physics Problems?

[Coldchillin]

http://img175.imageshack.us/img175/2448/picture1wt8.png

I am having trouble deciding when to use the static and kinetic frictions and what to do about this problem. Thanks for any help!

 

[Doc Al]

If the surfaces slip, then you have kinetic friction; if they don't, it's static friction.

Start by figuring out if it's possible for the block to not slip on the slab.