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Mechanical Energy, Potential Energy, Kinetic Energy, Momentum, Impulse, Work, Power, Conservation of Energy and Momentum

This chapter discusses the concepts of mechanical energy, potential energy, kinetic energy, momentum, impulse, work, power, and conservation of energy and momentum. It provides equations and examples of how these concepts apply in various scenarios. The chapter also explores elastic and inelastic collisions and their impact on momentum.

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Mechanical Energy, Potential Energy, Kinetic Energy, Momentum, Impulse, Work, Power, Conservation of Energy and Momentum

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  1. Energy Chapter 3 pp. 53-75

  2. Mechanical Energy- • Potential energy – • energy stored in an object due to its position • Kinetic energy- • energy in motion

  3. Potential Energy- • Equation- • PE = mgh • m - mass • g - acceleration. of gravity • h - height

  4. Kinetic energy- • Equation • KE = ½ mv2 • m – mass • v - velocity

  5. Conservation of Energy-TE=PE+KE The total amount of energy always stays the same it just changes forms! As they fall potential energy decreases and kinetic energy increases!

  6. Momentum- • the product of the mass of an object and its velocity

  7. Equation- m = mv (momentum = mass x velocity) mis called mew. We use it so there is not two m’s in the equation

  8. 1.) Does a parked car have momentum? • No, there is no velocity.

  9. A truck because it has more mass 2.) What has greater momentum a truck at 30 mph or a car’s at 30 mph?

  10. Apply to egg drop! • What is the potential energy of a 0.05 kg egg at a height of 4 meters?

  11. No calculation required! • What is the potential energy of a 0.05 kg egg at a height of 4 meters? • Based on conservation of energy what is the kinetic energy of the egg just before it hits the ground (height=0)?

  12. Tough algebra, you can do it! • What is the potential energy of a 0.05 kg egg at a height of 4 meters? • Based on conservation of energy what is the kinetic energy of the egg just before it hits the ground (height=0)? • What is the speed of the egg just before it hits the ground?

  13. Finally momentum! • What is the potential energy of a 0.05 kg egg at a height of 4 meters? • Based on conservation of energy what is the kinetic energy of the egg just before it hits the ground (height=0)? • What is the speed of the egg just before it hits the ground? • What is the momentum of the egg just before it hits the ground?

  14. Impulse- • The product of force acting on an object and the time during which it acts.

  15. Equations- • I = Ft = mv • (Impulse = Force x time) • (Impulse = change in mass x velocity) • I = µ • Impulse = change in momentum

  16. Impulse- (cont.) • Impulse = µ and is therefore constant • The force is dependant on the time applied • Short time means large force • I = Ft • Long time means small force • I = F t

  17. Review(you should have all these equations)

  18. Work- • Equation- • W = fd • (Work = force x distance) • More weight or more movement means more work was done

  19. 1.) How much work did a mover do if he lifted a 500 N box to a shelf that was 4 m high? • W = fd • = 500 N X 4 m • = 2000 N-m • = 2000 J (Joule) • A joule is a measurement of energy just like calories. (the amount of energy in food)

  20. Power- The time rate of work • Equation- • P = w/t • Power = work ÷ time

  21. Lets compare some athletes.

  22. ALWAYS USE A SPOTTER WHEN LIFTING!

  23. At nearly 7 feet 9 inches tall, with size 19 feet, Chinese basketball player Sun Mingming dreams of being in the NBA.

  24. If 2 people do the same job (the same amount of work), and one finishes faster, the person who did the job faster has more power.

  25. 8.) Mr. Foster and a small student run a 5K. Mr. Foster slows up so they cross the finish line in a tie. Who has more power? Mr. Foster, Of course! 9.) Why? Mr. Foster has more junk in the trunk and therefore did more work.

  26. 4.) Which of the following car crashes have a greater force?

  27. A.

  28. B.

  29. Answer: Collision A5.) Why? • The car was stopped faster in crash A because a pole is less forgiving than another car. • The force in B was carried out over a longer period of time.

  30. Conservation of momentum- Net momentum before collision = Net momentum after collision mV Mv Momentum before collision = Momentum after collision The velocity changes because the mass changes making it hard to see that momentum is conserved

  31. Collisions- • Elastic Collision- • colliding objects rebound without lasting deformation or generation of heat. • Inelastic Collision • deformation and generation of heat or both during a collision

  32. 6.) Are these collisions elastic or inelastic?

  33. 7.) Are these collisions elastic or inelastic?

  34. 3.) What is the momentum of a 80 kg jogger that is running 1 m/s? • Answer: m = mv • m = 80 kg • v = 1 m/s • 80 x 1 = 80 • 4.) m = 80_________? Kg-m/s

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