So.. I have an ideal linear spring that streches 20 cm when a 40g mass is hung from it. The spring is then mounted horizontally on a frictionless surface (screams conservation of energy/momentum) and a 60g mass is attached to it. The 60g mass is then displaced 20cm from equilibrum and released. Find the following: 1. frequency of oscillation 2. equation of motion for the mass 3. the speed and acceleration of the mass at +10 cm from equilibrium. 4. What would be the period of an external force that would drive the system at resonance and explain how I know this period is correct. So this is what I've chiseled at so far: I found the spring constant using hooke's law and got 1.96 N/m for k. Then I know that because its a spring it will obey Kfinal +Uspringfinal = Kinitial +Uspringinitial So pulling it means .5(1.96N/m)(.2m)^2 = .039 J of potential energy in the system. And since there wont be any other outside forces acting, the total energy for this system is going to be .039 J. The problem is, all I feel like I can get out of the problem is the basic puzzle pieces and I dont know how to put it all together. I'm trying to look things up on simple harmonic motion its just not clicking for me. Any leads/help?