1. The problem statement, all variables and given/known data On a horizontal floor there are 3 tiles on each other, 3 kg each. Which horizontal force should be applied in the middle tile, so that only it can be removed from the pile , when we know that the friction coefficient between the tiles is 0,3. 2. Relevant equations Ff=[PLAIN]http://upload.wikimedia.org/math/9/3/9/939974a71dda1b83cce5ab82a2d2cec1.png*N [Broken] 3. The attempt at a solution Ff=0,3* (3+3)*10=18N, but the solution is 90N.