1. The problem statement, all variables and given/known data http://streetrodjohn.home.comcast.net/~streetrodjohn/physics.jpg [Broken] A 1-kg block is pushed against a 4-kg block on a horizontal surface of coefficient of friction 0.25, as shown in the figure. Determine the minimum force needed to ensure that the 1-kg block does not slip down. Assume that the coefficient of friction at the interface between the block is 0.4. Hint: The two blocks exert equal and opposite forces on each other. 2. Relevant equations F=(A+B)a Ag=fs N=Ba Ag=[tex]\mu[/tex]Ba 3. The attempt at a solution In class we have done similiar problems, only with a frictionless horizontal surface. I don't know how to account for the horizontal coefficient of friction of .25 in this problem. Using the above equations and ignoring the horizontal coefficient of friction, I get this: a=(Ag)/([tex]\mu[/tex]B F=(((A+B)Ag)/([tex]\mu[/tex]B)) F=(((4+1)(1)(9.8))/((.4)(4))) F=30.62N Now how do I account for the horizontal coefficient of friction of .25? Thanks in advance for any help you can provide.