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# Energy 4

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### Energy 4

1. 1. ENERGY <ul><li>The Potential and Kinetic Chronicles </li></ul><ul><li>(The Law of Conservation of Mechanical Energy) </li></ul>
2. 2. What is Energy? <ul><li>Energy is the ability to do work </li></ul><ul><li>Potential Energy (PE), and Kinetic Energy (KE). </li></ul><ul><li>Energy is measured in Joules </li></ul>
3. 3. <ul><li>Energy cannot be created or destroyed, but can only be converted into different types of energy </li></ul>Law of Conservation of Energy Wind turbines transfer energy from the wind and convert it into electricity we can use.
4. 4. Potential Energy <ul><li>Is energy that is stored </li></ul><ul><li>Chemical energy </li></ul><ul><li>Nuclear energy </li></ul><ul><li>Mechanical PE </li></ul><ul><li>Gravitational PE (GPE) </li></ul>
5. 5. Example of a GPE Problem <ul><li>Gravitation PE problems have to do with an object and its position relative to the earths surface </li></ul><ul><li>PE = mgh = (mass)(gravity)(height) </li></ul>
6. 6. Example of a GPE Problem <ul><li>h=60m, g=9.81m/s 2 , m=2,000kg </li></ul><ul><li>PE= (60m)(9.81m/s 2 )(2,000kg)= 1,177,200 Joules </li></ul><ul><li>A roller coaster of 2 metric tons is sitting at the top of the track at a height of 60 meters. What is its PE? </li></ul><ul><li>use the PE=mgh formula </li></ul>
7. 7. Mechanical PE Problems <ul><li>have to do with stored energy within a spring </li></ul><ul><li>PE= 1/2kx 2 = 1/2(spring constant)( in spring length from equilibrium) </li></ul>
8. 8. Example of a MPE Problem <ul><li>A 4 gram rubber band with the spring constant of 4.3 F s /m is stretched a distance of 30 centimeters. What is the PE of the rubber band? </li></ul>
9. 9. Example of a MPE Problem <ul><li>Plug your information in the equation 1/2kx 2 formula </li></ul><ul><li>k= 4.3F s /m, x=30cm=.3m </li></ul><ul><li>PE s = .5(4.3 F s /m)(.3m)=.645 Joules </li></ul><ul><li>PE s =.645 Joules </li></ul>
10. 10. Kinetic Energy <ul><li>is energy of motion </li></ul><ul><li>Mechanical KE (MKE) </li></ul><ul><li>Radiant energy </li></ul><ul><li>Thermal energy </li></ul><ul><li>Electrical energy </li></ul>Kinetic Energy
11. 11. Example of a MKE Problem <ul><li>Mechanical KE problems involve objects that are in motion. </li></ul><ul><li>PE=KE or mgh=1/2mv 2 = 1/2(mass)(velocity 2 ) </li></ul><ul><li>If one knows the PE within a certain system, then one can find the variables such as v (velocity) </li></ul>
12. 12. Example of a MKE problem <ul><li>A roller coaster of 2 metric tons is sitting at the top of the track at a height of 60 meters has a PE of 1,177,200 . What is the velocity when it reaches the ground? </li></ul><ul><li>PE=KE, 1,177,200=1/2(2,000)(v 2 ) </li></ul><ul><li>sqrt(1,177,200/1,000)=sqrt(v 2 ) </li></ul><ul><li>v=34.3m/s </li></ul>
13. 13. PE of a spring problem <ul><li>A 4 gram rubber band with the spring constant of 4.3 N/m is fired after being stretched a distance of 30 centimeters it has a PE is .645 Joules. What is the velocity when it is fired? </li></ul><ul><li>PE s =KE, .645=.5(.004kg)(v 2 ) </li></ul><ul><li>sqrt(.645/.002)=sqrt(v 2 ) </li></ul><ul><li>v=18 </li></ul>