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Chapter 15

Chapter 15. Energy Assignments 15.1 Math Skills 1-3 p 448; AQs 1-9 p452 15.2 Math Skills 1-3 p 458; AQs  1-6 & 9-10. 15.2 Learning Targets for Energy Conversion and Conservation. Describe a situation in which energy is transformed from one form to another Explain how energy is conserved

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Chapter 15

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  1. Chapter 15 Energy Assignments 15.1 Math Skills 1-3 p 448; AQs 1-9 p452 15.2 Math Skills 1-3 p 458; AQs  1-6 & 9-10

  2. 15.2 Learning Targets for Energy Conversion and Conservation • Describea situation in which energy is transformed from one form to another • Explain how energy is conserved • Give an examplein which gravitational potential energyand kinetic energyare changed from one to the other • Solve equations that equate initial energy to final energy • Describe the relationship between energy and mass

  3. MP 1.A 10 kg rock is dropped & hits the ground at 60 m/s. Calculate PE before it was dropped. Ignore friction! • PE beginning = KE end • PE beg. = KE end = ½ m*v2 • PE beg.= KE end = 0.5*10 kg*(60 m/s)2 • PE beg. = 18,000 J

  4. MP 2.Diver w/mass = 70.0 kg stands atop 3.0 m high platform. Calculate PE on platform and KE as he enters water (ignore friction) • PE beginning = KE end = mgh • KE end = 70.0*9.9 m/s/s*3.0 m • KE end = 2100 J (? speed entering water) • KE = ½ m*v2 • 2100 J = 0.5*70.0 kg*v2 • 2100 = 35*v2(divide both sides by 35) • 60 = v2(take the square root of both sides) • V = 7.7 m/s

  5. MP 3.A pendulum w/ 1.0 kg weight is set in motion from 0.04 m above lowest point of path. What is KE at the lowest point? Ignore friction. • PE beginning (KE=0) = KE low point (PE=0) = mgh • mgh = 1.0 kg*9.8 m/s/s*0.04m • PE beginning = mgh = 0.4 J • PE beginning = KE end = 0.4 J

  6. 1. Describe how energy can be converted from one form to another in a wind-up toy • Elastic PE stored in the wound up spring is converted to KE as the spring unwinds and the toy moves.

  7. 2. State the law of energy conservation. • Energy cannot be created or destroyed (only transformed)

  8. 3. What energy change is taking place as an object falls in free fall? • PE is being converted into KE as it falls.

  9. 4. Explain Eintstein’s conclusion about the relationship between energy and mass. • Energy and mass are equivalent, and can be converted into one another

  10. 5. What type of energy change results when friction slows down an object? • Friction causes the conversion of kinetic energy into thermal energy

  11. 6. Describe the energy of a playground swing at its highest position. • The swing has maximum PE and no KE at its highest point.

  12. 9. A 0.15 kg ball is thrown into the air and rises to a height of 20.0 m. How much KE did the ball initially have? • KE beginning = PE end • KE beg. = PE end = mgh • KE beg.= PE end = 0.15 kg*9.8 m/s/s*20 m • KE beg. = 29 J

  13. 10. A 125 g steel ball with a KE of 0.25 J rolls along a horizontal track. How high up an inclined track will the ball roll if friction can be ignored? • KE beginning = PE end • KE beg. = PE end = mgh (solve for h) • KE / mg = h • h = 0.25 J / 125 kg*9.8 m/s/s • h = 0.20 m

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