Question

II. Relating work and changes in energy Experiment 2: The same blocks from Experiment 1 are now connected by a spring as shown at right. The blocks start at rest at time t3 with the spring in the relaxed position and come to rest at time t4, after moving a distance d0 from their initial positions with the same applied force as before (magnitude F0). A. Let system 2 consist of blocks A and B and the spring. What is the net work by external forces on system 2 during the interval from t3 to t4? Explain. B. Explain how your answer is inconsistent with Wnet ext = DK. C. Consider system 1 (the two blocks in Experiment 1) and system 2 (the two blocks plus spring in Experiment 2). In the table below, indicate whether each of the quantities is positive, negative, or zero for each system. Explain. D. State whether each of the statements below is consistent with your results above. If not, cite a specific case from the table that contradicts the student’s statement. Student 1: “The net work by external forces done on a system is always equal to the change in kinetic energy of that system.” Student 2: “In the absence of friction, the total energy of a system must remain constant. In other words, Kf + Uf = Ki + Ui.” Student 3: “The total energy of a system can change if something is doing work on that system. The net work done on a system by external forces is equal to the change in total energy of the system.”-- This is the previous page for experiment 3.

Answer 1

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