Tutorial Section 5.5 - Potential energy and choice of system A book of mass m starts from rest at a height h,- above the ground and descends in free fall to a height hf above the ground. Its speed at height hfis v,. 1. Using the system of the book and the earth together, a. Which of the forces on the book are internal forces? b. Are there external forces? c. What is the net work done by external forces on the system? 2. Using the system of the book alone, a. which of the forces on the book are internal forces? b. Are there external forces? c. What is the net work done by external forces on the system? 3. Fill out the following table: System of book & Earth System of book alone Change in kinetic energy of the book between initial and final locations a. What physical quantities are needed to calculate kinetic energy? b. Is it possible to measure experimentally these physical quantities? 6. Should the choice of system change the value of the book's kinetic energy? 4. What is the change in gravitational potential energy for this problem in a. the system of the book and the earth? b. the system of the book only? 5. Assume the earth's change in velocity is so small that its kinetic energy is constant\". What is the change in kinetic energy of the book-earth system? [:1 Checkpoint. Please continue working. 6. Use the table below for questions 6-10. In physics, one important tool we have is doing the same problem in multiple ways to check our result. Below, consider the same problem as above, but now use the other choice of system (e.g. book only). Fill in the table below with the change in each value from the initial position to the final osition. Esysfem wexf (on Q System system by (heat exchanged Esystem Esystem external between system forces) and external world) book only AKEbook = book and AKEbook AKEearth a 0 7. Look at the values in the table for the last question (AKE, APE, and Wm). Explain whether these do or do not make sense to you. Be sure to double-check your signs. 8. In your table, 4 This is a consequence of the conservation of momentum, which we will cover later in this course, and choosing the reference frame of the earth. Do the two systems have the same change in kinetic energy? Do the two systems have the same change in total energy? c. If you got different answers for the questions above, explain how it is possible for systems to gain different amounts in total energy but have the same change in kinetic energy? Is the law of conservation of energy violated? 53'5\" 9. Complete the following explanation given your values from above: In the book-only system, a. the change in the system's total energy (AE5y5,em) is (circle one: zero, positive, negative) b. the book's increase in kinetic energy is due to (circle all that apply) a decrease in potential energy of the system an increase in the potential energy of the system positive work done by exactly one external force on the system positive work done by more than one external force on the system positive work done by the system on surrounding objects In the book-earth system, a. the change in the system's total energy (AEsys,em) is (circle one: zero, positive, negative) b. the book's increase in kinetic energy is due to (circle all that apply) a decrease in potential energy of the system an increase in the potential energy of the system positive work done by exactly one external force on the system positive work done by more than one external force on the system positive work done by the system on surrounding objects 10. A student makes the following comment. Do you agree or disagree with this student? Hint: consider your answers from in section 2. Student: \"When we consider the system of the book and the earth, gravity does not do work. However, when we consider the system of the book only, gravity does work. How is it possible gravity does work in one case but not in the other?&quot