# ENERGY_1_

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```					                ENERGY
-WORK
-TRANSFORMATIONS

HTTP://TEACHERTUBE.COM/VIEWVIDEO.PHP?VIDEO_ID
=127812
Kinetic Energy

 In motion (has velocity)
 ½ mv2
UNIT: Joules

Velocity more than mass
Potential Energy

 Not moving: contain energy
 In Joules
 Gravitational Potential Energy: mgh
 Elastic Potential Energy:
Mechanical Energy

 PE + KE
Work
 Forces change based on Transformation of energy
 Only the force parallel to displacement is doing
work (NET W=NET F x d x cos angle)
 W=Fd (mass and acceleration of an object in a
direction times the distance the force is being
applied)-UNIT: JOULE (Nm)

 DERIVE:        2ad=vf 2-vi2   (Big Blue on the board)
Practice Problems

1.   A shopper in a supermarket pushes a cart with a
force of 35 N directed at an angle 25 degrees
downward from the horizontal. Find the work
done by the shopper on the cart as the shopper
moves along a 50.0 m length of side?

1600 J
1. If 2.0 J of work is done in raising a 180 g apple,
how far is it lifted?

1.                 1.1M
Work cont….

 Scalar
 Positive-same direction as displacment
 Negative-direction opposite (friction)
Kinetic Energy!

 Has mass and is moving
 Scalar
 Joule

WORK-KINETIC ENERGY THEOREM:
Wnet=Change in KE            (1/2)
KE Practice Problems
1. A 7 kg bowling ball moves at 3 m/s. How much KE
does the bowling ball have? How fast must a 2.45 g
ping pong ball move in order to the same KE as the
bowling ball? Is that realistic?
KE=31.5 J
V = 160 m/s
NO
A person kicks a 10 kg sled, with an Vi =2.2m/s. How far
does the sled move, if the coefficient of Fk b/t the sled
and ice is 0.1?

2.4 m
Potential Energy

 Based on the position relative to another location
 GPE=mgh (only in free fall near Earth)
 EPE=1/2kx2 (relaxed length 
compressed/stretched length)
   k=spring constant (N/m)
PE Practice Problems:

1.   A 70 kg bungee jumper has a cord 15 m long. He
jumps off a bridge from a height of 50 m. When he
finally stops the cord has stretched to 44 m.
Bungee cord has a k of 71.8 N/m, what is the total
PE relative to the water when the man stops
falling?

2.                                3430 J
 http://videos.howstuffworks.com/

```
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 views: 3 posted: 12/7/2012 language: Japanese pages: 13