• A large chunk of ice with a mass of 15-kg falls from a roof 8.0-m above the ground. Find the KE and the speed when it reaches the ground.

• What is the speed at the halfway point (@ 4 m)?

Bellwork

Conservation of Energy

As long as the system is closed so that objects do not move in and out, and the system is isolated

from outside forces, then energy can only change form.

Mechanical Energy• In a system, it is the sum of KE + PE

depending on the situation.

• Can be all KE or all PE, or a combination of both

• KE = 1/2 mv2

• GPE = mgh

• GPE is also written as Ug

• A 75-kg skier starts from rest at the top of a 45-m hill, goes down the hill, then back up a 40-m hill. Both heights are measured from the valley floor straight up. How fast was the skier moving at the bottom of the valley? What is the skier’s speed at the top of the next hill?

Remember the combustion engine?

• Heat

• Friction

• Air resistance

• Sound

• Resisting/changing motion

• Powering other mechanical parts

Kinds of Energy•Mechanical – energy used to physically move things •Radiant – light, radio, UV, etc.•Electricity – electrical energy•Heat/Thermal – energy moving from warmer to colder things•Chemical – energy of making and breaking chemical bonds•Nuclear – energy within the nucleus of an atom [fusion/fission]•Sound – energy of sound waves

Chemical KineticPotential RadiantNuclear SoundElectrical Heat/Thermal

Construct a scenario in which at least 6 of these energies are used. Be creative! Label each energy transfer.

Example: Using a photovoltaic cell (radiant to electrical) to power a fan (electrical to kinetic) that has a looped rope tied to

it spinning an electrical generator (kinetic to electrical) to power a radio (electrical to sound).

To be collected at the end of class.