A closed system has many quantities that don't change. The position of the center of mass moves at a constant speed in a straight line - which means that there is a reference frame where the center of mass does not change. Sometimes this is a very good way to examine a process. The total energy doesn't change, it just transfers between the objects in the system. The total momentum doesn't change, it just transfers between objects in a system. This situation investigates these properties. (0) Initial Position (1) Expansion Process (Spring - Friction) (1) Launch Position (II) Stopping Process (Friction) (2) Final Position In this problem, you will find how far two objects will separate after they are forced by a spring to move away from each other by the expansion of a spring. The process is to first compress the spring sufficiently that it will fully expand afterwards, adding energy to the system, then after letting go, the spring will expand in a second process that gives kinetic energy to the blocks. But, for the blocks to stop, the blocks rubbing against the surface they slide along must create friction, which steals energy not only after the blocks detach from the spring and move on their own, but also when the spring is expanding. So this will also have to be accounted for. In particular, the block on the left side has a mass of 140 g and block on the right side has a mass of 415 g. The spring has a stiffness of 60 kg/s2 and is compressed by 22 cm from its equilibrium length is38 cm. As the blocks move along the surface of a table, they frictional force has a coefficient of kinetic friction of 0.61. Part 2 of 4 - Situation at Launch When the spring is release, it expands, and when it reaches its equilibrium length, the two blocks start to move away from each other. Before we determine the velocities, we need to look at the configuration at the end and find how much energy is lost to friction. First, determine the forces of friction on the two blocks. These are the external forces on the system, and they will determine the change in the center of mass of the system. (a) What is the frictional force on the block? f = 0.837 N (b) What is the frictional force on the block? fr = 2.5 N X (c) What is the net force on the block? EF = 1.645 N This lets you find the change in the momentum over the time it takes the spring to expand, if you know that it takes 96 ms, as well as let's you find the distance that the center of mass has moved over that time. (d) What is the change in momentum? AP = 0.1579 kg m. X (e) What does this mean the final velocity of the system is? Vsys = (f) This should give you enough information to determine the position of the system's center of mass at launch. Xc