1. The problem statement, all variables and given/known data Block A, with mass mA, is initially at rest on a horizontal floor. Block B, with mass mB, is initially at rest on the horizontal top surface of A. The coefficient of static friction between the two blocks is μs. Block A is pulled with a horizontal force. It begins to slide out from under B if the force is greater than: A. mA*g B. mB*g C. μs*mA*g D. μs*mB*g E. μs(mA +mB)g Ans: E 2. Relevant equations Ff(static, max) = μs*NormalForce; 3. The attempt at a solution So the answer is already given as E, but I really want to understand this. I'm confused on a couple of things. So if we pull on A too hard, then B will fall out behind it. Does this mean that the force of static friction is acting in the direction of the applied force F? And the normal force acting on mass B is just mB*g correct? That's all I got. I'm a little stuck from there. Any help would be great. Thanks a lot ahead of time.