1. Physics 11 Energy 3 – Work, Kinetic, Potential Energy Mr. Jean

2. The plan: Video clip of the day Work to Kinetic to Potential Work to Potential to Kinetic

5. ENERGY = JOULES What I would like to accomplish with this example is to show you (and prove to you) that the unit joules are the same for Work, Potential Energy, and Kinetic Energy

6. Situation: A 2.5 kg brick is pick up off the ground. It is raised 1.5 meter, it stays there for 5 seconds, then dropped back to the ground.

7. Work: Calculate the work involved with lifting the brick. Work = Force x Distance

8. Work: Calculate the work involved with lifting the brick. Work = Force x Distance Work = (2.5kg)(-9.81m/s 2 ) x 1.5m Work = 36.79 J

9. Potential Energy: Calculate the potential Energy of a brick which is resting 1.5 meters in the air. E g = mgh

10. Potential Energy: Calculate the potential Energy of a brick which is resting 1.5 meters in the air. E g = mgh E g = (2.5kg) (-9.81)(1.5m) E g = 36.79 N m

11. Kinetic Energy: After the brick is released calculate the kinetic energy as the brick hits the ground. E k = 0.5(m)(v 2 )

12. Kinetic Energy: E k = 0.5(m)(v 2 ) v 2 = v 2 + 2ad v 2 = 0 + 2(-9.81m/s 2 )(1.5m) v 2 = 29.43 m 2 / s 2 E k = 0.5(2.5kg)(29.43 m 2 / s 2 ) E k = 36.79 J

13. Summary: Work = 36.79 J Potential Energy = 36.79 J Kinetic Energy = 36.79 J The joules are the same when looking at these three formulas.

14. Conservation of Energy: E k1 + E p1 + E e1 = E k2 + E p2 + E e2 E k1 = kinetic energy before event (J) E p1 = gravitational potential energy before event (J) E e1 = elastic potential energy before event. (J) E k2 = kinetic energy after event (J) E p2 = gravitational potential energy after event (J) E e2 = elastic potential energy after event. (J)

15. Example: Roller Coaster Awesomeness: Welcome to the Lawyer Proof Pain-0-rama 2000 Theme Park. The star attraction of this theme park is a roller coaster which has an abrupt end. Calculate the potential energy, kinetic energy and velocity at the various locations.

17. 1 ) E k1 + E p1 + E e1 = E k2 + E p2 + E e2

18. 2) E k1 + E p1 + E e1 = E k2 + E p2 + E e2

19. 3 ) E k1 + E p1 + E e1 = E k2 + E p2 + E e2

20. To do: Questions –P.287 1 to 4 Reading: –P.280 - 287 (Conservation of Energy) –P.255 – 261 (Springs and Elastic Energy) Next week springs on Monday Spring Lab Tuesday Conservation of Energy work Wed-Thursday