1) The coefficient of static friction is 0.60 between the two blocks in figure. The coefficient of kinetic friction between the lower block and the floor is 0.20. Force F causes both blocks to cross a distance of 5.0 m, starting from rest. What is the least amount of time in which this motion can be completed without the top block sliding on the lower block? Please Register or Log in to view the hidden image! Let A=top block, B=bottom block There are 4 forces acting on the block A: Gravity, Normal force (B on A), F (the applied force), and static friction (B on A) There are 5 forces acting on the block B: Grviaty, Normal force (earth on B), normal force (A on B), kinetic friction (earth on B), and static friction (A on B) Fnet on B=static friction (A on B)-kinetic friction (earth on B)=(mass of B)(acceleration) and then find time using kinematics. Using this method, I got an answer of 1.75s and this is correct according to my textbook. But this is not making sense to me. If the system is accelerating, then block A must be accelerating, i.e. net force on A should be to the right, and this means the applied force F is greater than the static friction of B on A. But if the applied force is greater than static friction, kinetic friction applies instead of static friction, right? If so, then block A is sliding on block B and I am running into terrible trouble on making sense of this problem... Can someone please explain and help me making sense of this scenario? Thank you!