1. The problem statement, all variables and given/known data See: http://www.aapt.org/physicsteam/2010/upload/2010_FmaSolutions.pdf #10 EDIT: There are several constants. 2. Relevant equations F = ma Ff = μN 3. The attempt at a solution First: Draw a free-body diagram for block 2 (the bottom block) Up: Normal force from floor pushing on block 2 Down: weight of block 1 on block 2 Down: weight of block 2 down Right: Force F Left: Force of Friction Ff Up forces = Down forces N = m1g + m2g N = g(m1 + m2) Ff = μg(m1+m2) F_y = 0 F_x = F_net so Fnet = F - Ff m2a = F - ug(m1+m2) a = (F - ug(m1+m2)/ m2 This is the wrong answer. The answer says it should be 2m1 + m2 not m1 + m2. Why is this?