A block of mass M₁ = 3.5 kg moves with velocity v₁ = 6.3 m/s on a frictionless surface. It collides with block of mass M₂ = 1.7 kg which is initially stationary. The blocks stick together and encounter a rough surface. The blocks eventually come to a stop after traveling a distance d = 1.85 m . What is the coefficient of kinetic friction on the rough surface?

μ_k =