CONSERVATION OF ENERGY

11.2 notes

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.

Example1

Example 2

Example 3

All mechanical energy = 100%

So, if you calculate that 42% of the energy a falling object has is kinetic energy, then ________% must be potential.

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

New Formula (kinda)

Kbefore + Ugbefore = Kafter + Ugafter

Otherwise known as…

1/2mv2 + mgh = 1/2mv2 + mgh

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?

Sketch it

List the variables

m = 85 kg h = 4 m l = 20 m

Other things we know…

Kinetic energy before is…Potential energy after is…

Come on, think!

Kb + Ugb = Ka + Uga

0 + (85)(9.8)(4) = 1/2 (85)v2 + 0

v2 =

v =

Does his speed depend on his mass?

Does his speed depend on the vine’s length?