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Work

Work. When a force acts upon an object to cause a displacement of the object, it is said that work was done upon the object. There are three key ingredients to work:. cause. force. displacement.

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Work

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  1. Work When a force acts upon an object to cause a displacement of the object, it is said that work was done upon the object. There are three key ingredients to work: cause force displacement In order for a force to qualify as having done work on an object, there must be a displacement and the force must cause the displacement.

  2. Work Examples A horse pulling a plow through the field A father pushing a grocery cart down the aisle of a grocery store A weightlifter lifting a barbell above his head

  3. “Energy” Mechanical energy is the energy which is possessed by an object due to its motion or its stored energy of position Kinetic energy : is the energy of motion Potential Energy : an object can store energy as the result of its position!

  4. Problems? W=F x d W=F x d cos 300 W= F x d =100N X 5m = 100N X 5m X .87 =15Kg(10m/s2) X 5m =500 J = 413 J = 750J

  5. Gravitational Potential Energy • After an object has been lifted to a height, work is done. PE = W= F x d= mah Energy of Position PE=mgh

  6. GravitationalPotential Energy Potential Energy is maximum at the maximum HEIGHT Problems: How much potential energy is lost by a 5Kg object to kinetic energy due a decrease in height of 4.5 m PE=mgh PE = (5Kg)(10 m/s2)(4.5 m) PE = 225 Kg m2/s2 PE = 225 J

  7. Problem With GPE A 60 kg skier starts off from rest at the top of the hill 10 m high: • How much PEG does the skier have at the top?

  8. Problems with GPE A 1000 kg train car moves from point A to point B, and then to point C. What is the Potential Energy at Points A, B and C?

  9. Roller Coaster PE=mgh PE=1000kg(9.8m/s2) (10m)

  10. Kinetic Energy The energy of motion DKE = W= F x d= mah=1/2 mv2 Find the kinetic energy of an 4 Kg object moving at 5m/s. KE = 1/2 mv2 KE = ½ (4Kg)(5m/s) 2 KE = 50 Kg m 2 /s 2 KE = 50 J

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