1. The problem statement, all variables and given/known data Two 3.0 kg blocks on a level frictionless surface are connected by a spring with spring constant 1000 N/m. The left block is pushed by a horizonal force F to the right. At time t=0 seconds, both blocks are moving with velocity 3.2 m/s to the right. For the next second, the spring's compression is a constant 1.5 cm. What is the magnitude of F during that 1.0 s interval 2. Relevant equations KE=.5*m*v^2 SPE=.5*k*(delta x)^2 F=(delta p)*(delta t) change in energy = force * distance 3. The attempt at a solution I tried to setup the following: Ei= .5*6kg*3.2^2 and Ef=Ei+F*d=.5*m*v1^2+.5*m*v2^2 +.5*k * (delta x)^2 Now I know everything about the spring potential energy at the end and the total energy (kinetic) at the beginning. But I guess the biggest problem I'm having is that I do not know the final velocities of either of the 2 blocks. I tried using conservation of momentum to relate them but got a much bigger mess with no obvious way to simplify. Would considering the center of mass of the 2 block system help? If I have the acceleration of the center of mass can I do something with that? Is this even the right approach at all? No matter what I do I get like 1 equation with 3 unknowns! Please help.