A 1.2 kg cart slides eastward down a frictionless ramp from a height of 1.8 m and then onto a horizontal surface where it has a head-on elastic collision with a stationary 2.0 kg cart cushioned by an ideal Hooke’s law spring. The maximum compression of the spring during the collision is 2.0 cm. (5.4) (a) Determine the spring constant. There were more parts to this question, however, I just need help with this portion of it. Law of Conservation of Energy: Et1 = Et2 Force of Spring formula: F= kx Kinetic Energy, Gravitational Potential Energy, Elastic Potential Energy formulas will come in handy too. So in terms of solving this, I though I should find the final speed of the 1.2 kg cart which will end up being the initial velocity right before the collision takes place. I got 5.94 m/s for that (mgh = 1/2mv^2). Using this speed, how should i incorporate it to get the "k" value? I could use conservation of energy for the second block... (1/2mv^2 = 1/2kx^2) But I would need the speed for block 2, which is tricky because it was stationary initially.. The answer for the k value is 6.6x10^4 N/m. Let me know what you guys suggest!