1. The problem statement, all variables and given/known data An object of mass, m, is traveling on a horizontal surface. There is a coefficient of kinetic friction, mu , between the object and the surface. The object has speed, v, when it reaches x=0 and encounters a spring. The object compresses the spring, stops, and then recoils and travels in the opposite direction. When the object reaches x=0 on its return trip, it stops. Find k, the spring constant. Express k in terms of mu , m, g, and v. 2. Relevant equations Work-energy theorem 3. The attempt at a solution I know that the work-energy theorem must be used in this problem. What is throwing me off is the friction i think because of the x and because it's a two stage problem? Not quite sure. Any help would be much appreciated.