1. Energy and Work
Chapter 28: 1-3

2. 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?

3. 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

4. How can we isolate a system?

5. 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

6. 10.4 Work
Special Special Case: F constant and in direction of the displacement.
Units: 1 N•m=1 J = 1 Joule

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

8. 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?

9. 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?