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UNIT 4 Work, Energy, and Power

UNIT 4 Work, Energy, and Power. ConcepTest 6.5a Kinetic Energy I. By what factor does the kinetic energy of a car change when its speed is tripled?. 1) no change at all 2) factor of 3 3) factor of 6 4) factor of 9 5) factor of 12. ConcepTest 6.5a Kinetic Energy I.

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UNIT 4 Work, Energy, and Power

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  1. UNIT 4Work, Energy, and Power

  2. ConcepTest 6.5aKinetic Energy I By what factor does the kinetic energy of a car change when its speed is tripled? 1) no change at all 2) factor of 3 3) factor of 6 4) factor of 9 5) factor of 12

  3. ConcepTest 6.5aKinetic Energy I By what factor does the kinetic energy of a car change when its speed is tripled? 1) no change at all 2) factor of 3 3) factor of 6 4) factor of 9 5) factor of 12 Since the kinetic energy is 1/2 mv2, if the speed increases by a factor of 3, then the KE will increase by a factor of 9. Follow-up: How would you achieve a KE increase of a factor of 2?

  4. Wednesday November 9th POTENTIAL ENERGY

  5. TODAY’S AGENDA Wednesday, November 9 • Potential Energy • Hw: Practice C (All) p168 UPCOMING… • Thur: Conservation of Mechanical Energy • Fri: Bowling Ball Demo • Mon: Problem Quiz 1

  6. Section 2 Energy Chapter 5 Potential Energy • Potential Energy is the energy associated with an object because of the position, shape, or condition of the object. • Gravitational potential energy is the potential energy stored in the gravitational fields of interacting bodies. • Gravitational potential energy depends on height from a zero level. PEg= mgh gravitational PE = mass  free-fall acceleration  height

  7. Section 2 Energy Chapter 5 Potential Energy, continued • Elastic potential energy is the energy available for use when a deformed elastic object returns to its original configuration. • The symbol k is called the spring constant, a parameter that measures the spring’s resistance to being compressed or stretched.

  8. Section 2 Energy Chapter 5 Elastic Potential Energy

  9. Section 2 Energy Chapter 5 Sample Problem Potential Energy A 70.0 kg stuntman is attached to a bungee cord with an unstretched length of 15.0 m. He jumps off a bridge spanning a river from a height of 50.0 m. When he finally stops, the cord has a stretched length of 44.0 m. Treat the stuntman as a point mass, and disregard the weight of the bungee cord. Assuming the spring constant of the bungee cord is 71.8 N/m, what is the total potential energy relative to the water when the man stops falling?

  10. Section 2 Energy Chapter 5 Sample Problem, continued Potential Energy 1. Define Given:m = 70.0 kg k = 71.8 N/m g = 9.81 m/s2 h = 50.0 m – 44.0 m = 6.0 m x = 44.0 m – 15.0 m = 29.0 m PE = 0 J at river level Unknown:PEtot= ?

  11. Section 2 Energy Chapter 5 Sample Problem, continued Potential Energy 3. Calculate Substitute the values into the equations and solve:

  12. END

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