Conservation of Energy

1. Conservation of Energy 11.2 notes

2. Mechanical Energy = K + Ug • In other words, all the kinetic energy in a system plus all the potential energy of a system is total amount of mechanical energy in the system.

3. Example1

4. Example 2

5. Example 3

6. All mechanical energy = 100% • So, if you calculate that 42% of the energy a falling object has is kinetic energy, then ________% must be potential.

7. Part 2 All the kinetic energy plus all the potential energy before something happens equals all the kinetic energy plus all the potential energy after the event. This is called Conservation of Energy

8. New Formula (kinda) Kbefore + Ugbefore = Kafter + Ugafter

9. Otherwise known as… 1/2mv2 + mgh = 1/2mv2 + mgh

10. Example problem 1 • Tarzan, mass 85 kg, swings down on the end of a 20m vine from a tree limb 4.0 m above the ground. • How fast is Tarzan moving when he reaches the ground? • Does your answer depend on Tarzan’s mass? • Does your answer depend on the length of the vine?

11. Sketch it

12. List the variables • m = 85 kg • h = 4 m • l = 20 m

13. Other things we know… Kinetic energy before is… Potential energy after is… Come on, think!

14. Kb + Ugb = Ka + Uga 0 + (85)(9.8)(4) = 1/2 (85)v2 + 0 v2 = v =

15. Does his speed depend on his mass?

16. Does his speed depend on the vine’s length?