450 mm 75 mm 400 mm- B 150 N PROBLEM 13.31 A 5-kg collar A is at rest on top of, but not attached to, a spring with stiffness k₁ = 400 N/m; when a constant 150-N force is applied to the cable. Knowing A has a speed of 1 m/s when the upper spring is compressed 75 mm, determine the spring stiffness k₂. Ignore friction and the mass of the pulley.