I have struggled with this question. I don't understand what do especially that the question says inelastic but there is a spring. A mass of 12 kg is sliding along a frictionless surface at a speed of 5 m/s. It collides perfectly inelastically with a stationary mass of 24 kg which is attached to a spring. If the spring constant is 225 N/m, where are the stuck-together masses 3 seconds after the collision? I know momentum before collision is 12*5= 60 But I don't know what to do from here ... I know momentum has to be conserved but not energy but I am having trouble understanding what can the next step be. I hope someone can help me.