1. The problem statement, all variables and given/known data The coefficient of static friction is 0.55 between the two blocks in Figure P8.32. The coefficient of kinetic friction between the lower block and the floor is 0.20. Force FT causes both blocks to cross a distance of 5.0 m, starting from rest. What is the least amount of time in which this motion can be completed without the top block sliding on the lower block? http://img27.imageshack.us/img27/5121/p832.gif [Broken] 2. Relevant equations I think a few of these may be unnecessary, if I knew exactly how the problem worked I'd probably know why. a=accel v=velocity Δx=displacement Δt=change in time fk=μkn and fk=μkm7g and fs=μsm4g F=ma vf=vi+aΔt Δxf=Δxi+viΔt+.5a(Δt)2 vf2=vi2+2aΔx 3. The attempt at a solution (Verbal Explanation) Realized that the greatest force would have to be equal to static friction created by 4kg block. Set greatest force static friction could produce to the tension force. Used tension force to find acceleration produced across floor with a 7kg block. Calculated final velocity using acceleration and displacement. Calculated time using final velocity and acceleration. m4=4kg mass m7=7kg mass Using the top box's maximum static friction I found the force... fs=μsm4g=FT ..to be 21.56N, I then plugged that force into my acceleration equation... ax=((F/m7)-μkg) ..which gave me 1.12m/s2 as the acceleration across the 5m displacement I then used that acceleration in the kinematic equation... vf2=vi2+2aΔx ..giving me a vf of 3.35m/s ..finally I used the equation vf=vi+aΔt to solve for time, giving me 2.99s, which turned out to be wrong. Is my methodology incorrect or just my math somewhere along the way?