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Understanding Work, Energy, and Their Principles in Physics

This text outlines the fundamental concepts of work and energy in physics. It explains how work occurs when a force acts on an object to produce displacement, highlighting three key ingredients: cause, force, and displacement. Examples of work in real life, such as a horse plowing or a weightlifter lifting weights, reinforce these concepts. Additionally, it covers mechanical energy, kinetic energy, and potential energy, with equations to calculate gravitational potential energy and kinetic energy based on position and motion.

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Understanding Work, Energy, and Their Principles in Physics

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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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