1. The problem statement, all variables and given/known data A block moves along a frictionless surface with an initial velocity of 10 m/s. It contacts a spring of spring constant 350 N/m. Underneath the spring at and after the point of contact the ground is rough and applies a constant friction force of 45 N. The spring compresses 0.75 m before the mass stops. What is the mass of the block? 2. Relevant equations Ki + Ui = Kf + Uf 3. The attempt at a solution Ui and Kf are zero, so I had 1/2mv2 = 45 + 1/2kx2, but I'm not sure where to put the friction force in the equation. The answer is supposed to be 2.64 kg... Please help!