Physics 7A FNTs due DL 7 1) (extension) You have constructed an Energy-Interaction Model for physical phenomenon described in Activity 2.8. You are now going to reason with this to make sense of and to explain why Set B of the masses (the set with the smaller masses) moved faster than Set A. Here you will not be relying on your intuition, but on solid principles and logical argument. Comparing the changes in energies: a) Write down the total kinetic energy of the two masses (the sum of the KEs). During the process (from initial to final), does the total kinetic energy increase, decrease, or stay the same? How do you know? Is your response the same for both Set A and Set B? b) Write down the total potential energy of the two masses (the sum of the PEs). During the process does the total potential energy, decrease, or stay the same? How do you know? Is your response the same for both Set A and Set B? c) Compare the magnitude of the total change in PE of both masses that occurs during the process between Set A and Set B. Are the total changes the same or different? Explain. d) Compare the magnitude of the total change in KE of both masses that occurs during the process between Set A and Set B. Are the total changes the same or different? Explain. Creating a Solid Scientific Explanation: e) Using your responses to questions a)-d) develop a logical argument based on the Energy-Interaction Model that explains why the set of masses with smaller total mass move faster that the set with greater total mass, as long as the difference between the two masses in each set is the same. f) Using the expression you developed in Activity 2.8 B) 2), solve for the final velocity in terms of m, M, g, v, and d. Using this equation argue which set should be moving faster. Does your answer agree with your argument that you have developed in e) above? 2) (solidification) A 0.4-kg mass is attached to a spring that can compress as well as stretch. The mass and spring are resting on a horizontal tabletop. The spring constant is 50 N/m. The mass is pulled, stretching the spring 48 cm. The mass is then released, and the spring-mass system begins to oscillate. a) Construct a complete Energy-Interaction diagram to predict the speed of the mass as it passes a point that is a distance of 39 cm from its equilibrium point with the spring compressed? Assume the transfer of energy to thermal systems is negligible. b) Now assume the effects of friction are not negligible. When pulled back and released as before, the mass now reaches its furthest distance from equilibrium at 40 cm on the compressed side (before bouncing back again). Construct a complete Energy-Interaction diagram that could be used to determine the amount of energy transferred to thermal when going from the initial stretched position to where it first momentarily stops. Find the increase in thermal energy. 3) (solidification) A 55-kg skier skies down the smooth (frictionless) ski slope illustrated in the diagram. She pushes off at the top with a speed of 10 m/s. At the bottom (0 m), she comes to a stop by digging her skis in sideways. 30 m a)Construct a complete Energy-Interaction diagram to predict the speed of the skier 10 m when she is on the middle flat part (10 m). b) Repeat a) to find the speed of the skier at the bottom of the hill (before she starts stopping). c) Assuming that the snow where she comes to a stop is at a temperature of OC, and that all of the kinetic energy of the skier goes into melting the snow, construct a complete Energy-Interaction diagram to predict the amount of snow melted by the skier while stopping. d) Choose a different interval from the one you used in b), and solve again for the amount of snow melted when the skier stops. Is your answer the same as in b)? Continue to Next Page Unit 2: Applying Models to Mechan Phenomena DL 6