1. April 7, 2009 Study for 5 min for your quiz.
You need: Calculator and Writing Utensil
When you are done with quiz: Bring it up and pick up a note sheet for Energy!

2. Goals To explain different types of energy
To calculate potential and kinetic energy

3. Q: What is ENERGY? Energy is…. the ability to do work
a measure of how much work is done
a word to describe the power and effort of a force.
measured in Joules

4. ENERGY Energy is the ability to do work Doing work uses energy
An object can gain energy if work is done on it

5. Q: What is ENERGY? Two MAIN types of mechanical energy:
Potential energy
Kinetic Energy

6. Q: What is POTENTIAL ENERGY?
Potential Energy (PE) is stored energy
Coaster has PE when it is at the top of the hill. Even if it isn’t moving yet, it may if a force is applied and it begins to move

7. Q: What is POTENTIAL ENERGY?
Gravitational potential energy (GPE) is the energy of an object due to its position above the surface
GPE = mgh = wh
m=mass (in Kg)
g=acceleration due to gravity … 9.8 m/s2
h= height (in m)
w = weight (N)
UNITS:

8. “Homework”
Complete the Practice Problem for PE on your note sheet!

9. Equation: GPE = m x g x h h = 35 m m = 65 kg g = 9.8 m/s2 GPE = ?
PRACTICE PROBLEM: Find the PE of a rock climber as she climbs 35 m above the base of a cliff. Her mass is 65 kg.
Equation:
GPE = m x g x h
Given:
h = 35 m
m = 65 kg
g = 9.8 m/s2
GPE = ?
Solve: GPE =
65 kg x 9.8 m/s2 x 35m
=22,295 J

10. Q: What is KINETIC ENERGY?
Kinetic Energy (KE) is the energy due to an object’s motion
Active energy
A rock as it falls off of a cliff
Formula: KE = ½ * m * v2
m= mass (kg)
v = velocity (m/s)
UNITS:

11. PRACTICE PROBLEM: What is the KE of a 44 kg Cheetah running at 31 m/s?
Given:
m = 44 kg
v = 31 m/s
KE = ?
Equation:
KE = ½ * m * v2
Solve: KE =
(1/2) (44 kg) (31 m/s)2
21,142 J

12. Homework
Kinetic and Potential Energy WS