4/8/11
Post date: Apr 08, 2011 12:48:8 PM
Bell Ringer: A 3.00 kg Chihuahua is roller skating at 1.5 m/sec. a) How much KE does it have? b) If 50 N of forward force are applied to it over 5 meters, how much KE will it have? c) How fast does it move afterward?
Return and discuss quizzes
Conservation of energy notes
Energy can never be created or destroyed, but it does change forms and locations easily
Total energy in a system does not change
Ei = Ef
example: Car rolling down a hill
Energy flow diagrams
Since energy transforms so readily, it is useful to have a clear way to picture where the energy goes
Box energy type at each point, make notes in parentheses below boxes
Show energy transformations as arrows from one box to another.
Each box ends up with multiple arrows coming from it, can label each with a percentage to show efficiencies.
Almost all energy can be traced back to the sun (matter), and all matter can be traced back to the big bang (when it was transformed from energy into matter). Before that ... who knows?
example: ball rolling down a ramp
example: ball rolling through a loop
example: brick pendulum
example: Tom Hanks fire
How to solve conservation or energy problems
Draw free body diagram for time period of interest
Decide what types of energy are present in "initial" and "final" states
Write a conservation equation: (Initial energy type a) + (Initial energy type b) + (Initial energy type c) ... = (final energy type z) + (final energy type y) + (final energy type x) ...
Plug in numbers or equations for each energy type, and solve for unknowns.
example: Superman leaping a tall building in a single bound
P.230: 9-11 due Monday