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Energy. Energy is the ability to do work. Energy of motion is called kinetic energy . Energy unit is the Joule. Kinetic energy = ½ x mass x velocity 2 KE = ½ mv 2. If we have a mass of 2 and a velocity of 3, what is the kinetic energy? KE = ½ mv 2 KE = .5 x 2 x 3 2 KE =.5 x 2 x 9

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## Energy

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**Energy is the ability to do work.**• Energy of motion is called kinetic energy. • Energy unit is the Joule.**Kinetic energy = ½ x mass x velocity2**• KE = ½ mv2**If we have a mass of 2 and a velocity of 3, what is the**kinetic energy? • KE = ½ mv2 • KE = .5 x 2 x 32 • KE =.5 x 2 x 9 • KE = 9**The Work-Energy Theorem states that when work is done on an**object, its kinetic energy changes, and the work done equals the change in kinetic energy. • Work = change in kinetic energy**Work = KEf – KEi**• Since KE = ½mv2 • Work = ½ mfvf2 – ½ mivi2**If a 100 kg truck accelerates from 20 to 40 m /s. What work**is done by the engine? • Work = ½ mfvf2 – ½ mivi2 • Work = ½ 100x402 – ½ 100x202 • Work=.5x100x1600 - .5x100x400 • Work = 80,000 – 20,000 • Work = 60,000 J**Energy that is dependent upon height is called potential**energy. • Potential energy equation 1 = mass x gravity x height • Potential Energy = PE • PE = mgh**A ball is thrown up. At the top of the path, how fast is**the ball moving? • 0 m/s – Not moving • How much kinetic energy does the ball have at the top of the path? • 0 – since it is not moving**If the ball is thrown to a height of 5 meters and the ball**has a mass of 10 grams, what is the PE? • Which equation? PE = mgh or PE = wh • PE = mgh • PE = 10 g x 10 m/s2 x 5 m/s • PE = 500 J**If gravity is the only force causing the potential energy,**than the energy is called gravitational potential energy. • A system can also have potential energy due to a spring.**Potential energy that is stored in a spring is called**elastic potential energy. • The equilibrium of the spring is its unstretched position – where the spring has no force.**Equation for elastic potential energy = ½ (spring constant)**(spring displacement)2 • The spring constant is represented by k • The spring displacement or distance the spring is stretched is represented by x • PEelastic = ½ kx2**Spring constant of 180,000 and the spring is compressed .15**m, what is the elastic potential energy? • PEelastic = ½ kx2 • PEelastic = ½ 180,000 x .152 • PEelastic = ½ 180,000 x .0225 • PEelastic =2025 J**As a mass accelerates on a spring, the spring’s stored PE**is converted to kinetic energy. • When the mass reaches the equilibrium position where x = 0, the Potential energy = 0 and the kinetic energy is at the maximum.**The mass will continue to vibrate back and forth, changing**potential energy to kinetic energy until the mass stops moving. • This process with the mass vibrating right to left and back again, changing kinetic to potential and potential to kinetic is called simple harmonic motion.**When potential energy is converted to kinetic energy, what**forces take away some of the energy? • Friction, - Energy is transformed into heat • The law of conservation of energystates that in an isolated system, energy is conserved – it cannot be created or destroyed.**Total energy 1 = PE + KE**• Total energy 2 = mgh + ½ mv2**What is the total energy of a ball that has KE of 10 and PE**of 10? • Which Equation; TE = KE + PE or TE = ½ mv2 +mgh? • TE = KE + PE • TE = 10 + 10 • TE = 20**What is the total energy of a ball that has a mass of 250**and a height of 25 with a velocity of 40? • Which Equation; TE = KE + PE or TE = 1/2mv2 +mgh? • TE = ½mv2 +mgh • TE = ½ 250(40)2 + 250(10)25 • TE = ½ 250 (1600) + 250(10)25 • TE=200,000+62,500 =262,500 J

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