1. The problem statement, all variables and given/known data A block of mass 20kg sits on top of a block mass 50kg. The coeficent of static friction between the top block and the bottom block is .6, while the kinetic is .4. The bottom block is on a frictionless surface. The top block is pulled with a force of 200N. What is the acceleration of the bottom and top block? 3. The attempt at a solution I started out making it as a system, so that the system has a mass of 70kg and only 20kg accounts for the friction. So the friction would be 120N while not moving, and 80N after it has began to move. So with that being said, it appears that the top block would have a friction of 6m/s^2 because it would be (200N-80N)/20kg (i am using 10 for g at the moment). But what is the prupose of the static friction? Does the bottom block get pulled by the top block at the rate of static friction? I am not sure why static is in this problem, but my only guess would be for that.