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Energy Computer Lab

Energy Computer Lab. Mechanical Energy. Is the kinetic energy of the object + the all of the potential energy that the object has. Like all energy, Mechanical Energy is measured in Joules (J).

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Energy Computer Lab

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  1. Energy Computer Lab

  2. Mechanical Energy • Is the kinetic energy of the object + the all of the potential energy that the object has. • Like all energy, Mechanical Energy is measured in Joules (J)

  3. 1. What is the Mechanical energy of a football that has gravitational potential energy of 40 J and a kinetic energy of 500 J?

  4. 2. What is the Mechanical energy of a paperclip on a slinky that is hung vertically from a cliff? The clip has a KE of 40 J, a Gravitational Potential energy of 30 J, and an Elastic Potential energy of 15 J.

  5. Mechanical Energy is very useful in calculations, because it is always conserved. (For a given situation, the Mechanical Energy is always the same number of Joules)

  6. Mechanical Energy Example: Kermit is performing a graceful high dive. Shown below is a picture of Kermit’s dive:

  7. Mechanical Energy Example: Kermit is performing a graceful high dive. Shown below is a catalog of his PEg and KE at different points in his dive.

  8. Questions about previous slide: • 3. What is the Mechanical Energy that Kermit has at ANY point in his dive? • 4. If Kermit has a high KE, what is his PEg like? • 5. If Kermit has a high PEg, what is his KE like? • 6. If Kermit had a KE of 38 Joules, what would his gravitational potential energy be? • 7. If Kermit had a KE of 38 Joules, Label where he would be on the picture on the previous slide. (approximately, it doesn’t have to be exact)

  9. PEg = mgh KE = ½ mv2 Peelastic = ½kx2 • These equations can be used in conjunction with mechanical energy arguments in order to solve for specific quantities.

  10. Example: A 200 kg man walks off a diving board that is 50 meters above the water. What is his height at the point that he has a velocity of 10 m/s? • ME = PE + KE PE = mgh KE = 1/2mv2 • At the moment before he walks off, KE is zero, so ME = PE here. ME = mgh ME = 200 * 9.8 * 50 ME = 98,000 J. • The ME is the same everywhere. It is conserved. • At the point in question, ME = PE + KE 98,000 = mgh + ½ mv2 98,000 = 200 * 9.8 * h + ½*200*102 • Solve for h = 44.9 meters

  11. Questions • 8. A 45 kg rock is dropped off a cliff that is 80 meters above the ground. What is the height of the rock at the point that it has a velocity of 25 m/s? • 9. A 375 kg statue is dropped out of a helicopter that is 100 meters above the ground. What is the height of the rock at the point that it has a velocity of 17 m/s?

  12. Questions (similar to 8,9, except use PEelastic also) • 10. A Nerf toy shoots out foam balls. It has a spring constant (k) of 50,000 N/m. It is launched straight upward. The spring inside the launcher is compressed a total of .1 meter right before the .2 kg nerf ball is released. What is the velocity of the ball at a height of .6 meters? [ ANSWER: 50 m/s ]

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