I am wondering if someone could guide me on this. I am getting a vf of 4.6m/s, which can't be right, considering vi is only 3.8m/s. A box slides across a frictionless floor with an initial speed v = 3.8 m/s. It encounters a rough region where the coefficient of friction is µk = 0.7. If the strip is 0.52 m long, with what speed does the box leave the strip? My thoughts: F=µk*N=µk*g*m=6.867*m vi=3.8 m/s Using work-energy theorem: F*d = .5*m*vf^2 - .5*m*vi^2 6.867*d*m = m*(.5*vf^2 - .5*vi^2) m's cancel 6.867*.52 + .5*vi^2 =.5*vf^2 3.4335 + .5*(3.8)^2 =.5*vf^2 (3.4335 + 7.22)*2=vf^2 sqrt (21.307) = vf 4.62 = vf Ridiculous. What am I doing wrong?