Energy and Work Chapter 28: 1-3

Quiz 1. M1 = 0.473 kg, M2=1.343 kg, R=6.56cm 2. Cylinder: I = ½MR2 3. What is the I for each disk? 4. What is the initial angular momentum of each disk? 5. Is angular momentum conserved during this “collision”? 6. What must be true if L is conserved?

Energy and Energy Transfers Kinetic Energy Thermal Energy Chemical Energy Potential Energy Transfers: Work—transfer of energy by forces Heat—transfer of energy because of temperature differences

How can we isolate a system?

Conservation of Energy Isolated system: No energy exchanged between system and the rest of the universe. Energy exchanges occur between components of the systems inside the box isolating system. Alternatively

10.4 Work Special Special Case: F constant and in direction of the displacement. Units: 1 N•m=1 J = 1 Joule

Special Case: Constant force and a constant angle θ to the displacement. What happens if θ = 00

Problem 10.1 During an etiquette class you walk slowly and steadily at 0.20m/s for 2.5m with a 0.75 kg book balanced on top of your head. How much work does your head do on the book?

Problem 10.2 A 2.0 kg book is lying on a 0.75 m high table. You pick up the book and place it on a bookshelf 2.3m above the floor. How much work does your hand do on the book? (diagram) How much work does gravity do on the book?