Download Intro to Energy

Energy ­­ ability to do work.
Energy is a scalar.
General symbol for energy is E.
Energy is measured in Joules (J) 1
Forms of Energy
All forms of energy fall into 2 basic types H
C
H
Potential Energy
Kinetic Energy
stored energy
energy of motion
Chemical Energy
H
Nuclear Energy
Mechanical Potential Energy
Mechanical Kinetic Energy
Radiant Energy
Thermal Energy
Electrical Energy
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Mechanical Energy: Gravitational Potential Energy
Gravitational Potential Energy ­­ energy the object has due to its position in Earth's (or other planet's) gravitational field.
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PE = mgh
where
PE ­­ gravitational potential energy
m ­­ mass of the object
g ­­ acceleration due to gravity
h ­­ height of the object above the "zero" position 5
Problem Time!
Example 1: Legend has it that Isaac Newton “discovered” gravity when an apple fell from a tree and hit him on the head. If a 0.20 kg apple fell 7.0 m before hitting Newton, what was its change in PE during the fall?
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Example 2: A Mexican jumping bean jumps with the aid of a small worm that lives inside the bean. If a bean of mass 2.0 g jumps 1.0 cm from your hand into the air, how much potential energy has it gained in reaching its highest point? 7
Example 3: A flea gains 1.0x10­7J of potential energy jumping up to a height of 0.030 m from a dog’s back. What is the mass of the flea?
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Mechanical Energy: Kinetic Energy
Kinetic Energy ­­ energy of motion. Any object that has velocity possesses kinetic energy.
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KE = 1/2 mv
where
KE ­­ kinetic energy
m ­­ mass of the object
v ­­ velocity of the object
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What happens to the Kinetic Energy if
1. Mass doubles?
2. Velocity doubles?
3. Mass triples?
4. Velocity triples?
5. Mass doubles & velocity doubles?
6. Mass halves?
7. Velocity halves?
8. mf=mi/3 and vf=vi/3
9. mf=mi/4 and vf=vi/4
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Problem Time!
Example 1: The 2000 Belmont Stakes winner, Commendable, ran the horse race at an average speed of 15.98 m/s. If commendable and jockey Pat Day had a combined mass of 550.0 kg, what was their KE as they cross the finish line?
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Example 2: Missy Diwater, the former platform diver for the Ringling Brother's Circus had a kinetic energy of 15 000 J just prior to hitting the bucket of water. If Missy's mass is 50 kg, then what is her speed?
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