1. The problem statement, all variables and given/known data A sledge of mass m1 is pulled horizontally with a force F. On the sledge there is a body of mass m2 that can slide on the horizontal platform of the sledge with the friction coefficient μ. Another sledge of mass m3 is tied with a horizontal string of the body m2. Between the sledges and the snow the friction is negligible. Find the condition that is satisfied when the m2 body does not slide. 2. Relevant equations fs = μN T = [m2/(m1 + m2)]*F 3. The attempt at a solution I assumed that μ is the coefficient of static friction. If the m2 body is not to slide, the static friction between this body and the m1 sledge must be bigger than the tension in the string. The tension in the string should be: T = [m3/(m1 + m2 + m3)] * F and the static friction: f = m2gμ m2gμ > [m3/(m1 + m2 + m3)] * F This gives: μ > F/m2g * [m3/(m1 + m2 + m3)] but the book answers say that: μ > F/m2g * [(m3 + m2)/(m1 + m2 + m3)] What is wrong?