1. The problem statement, all variables and given/known data 2. Relevant equations sum of forces 3. The attempt at a solution So I tried summing the forces in the x-direction where m*a (block a) = -Ff + T = m(block a)*g*u + m*a(block b) + m*g(block b) where u is the coefficient of friction, T is the tension in the rope and Ff is the frictional force. I'm not, however, getting an answer on the multi choice list. Is there something I'm missing?