A box slides across a frictionless floor with an initial speed v = 3.5 m/s. It encounters a rough region where the coefficient of friction is µk = 0.6. a) What is the shortest length of rough floor which will stop the box? b) If instead the strip is only 0.41 m long, with what speed does the box leave the strip? I'm not sure how to start this problem. I'm kind of lost with work and energy. This is due tomorrow morning so any help is greatly appreciated. Thanks!