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Calculating Energy

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What did you notice about the TOTAL ENERGY during the skatepark lab? Total Energy does NOT change! The amount of KE, PE and THERMAL change, but always add up to the same total! THE LAW OF CONSERVATION OF ENERGY: Energy cannot be created or destroyed, it only changes forms

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Potential Energy Stored Energy

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Any energy that is STORED UP is Potential Energy! Gravitational PE –Determined by an object’s height Elastic PE –Stretching or Compression Chemical PE –Food (not yet eaten) –Gasoline (not yet burned) –Battery (not yet used)

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Gravitational PE Any time an object has height above a reference point. GPE = M*G*H –Mass (in kilograms) –G (acceleration due to gravity = 9.8 m/s 2 ) –Height (in meters) The UNIT for Energy is JOULE (J)!

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EXAMPLE 1 A 0.5-kg squirrel sits at the top of a 10- meter tall tree eating an acorn. How much Gravitational Potential Energy does the squirrel have? Step 1: Write the given information and the formula Step 2: Substitute the given values into the formula Step 3: Solve the problem (with units!) M = 0.5 kg H = 10 m G = 9.8 m/s 2 GPE = mgh GPE = 0.5kg x 9.8 m/s 2 x 10 m GPE = 49 Joules

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Practice on Your Own 1.Nijah drives her 1000-kg Mini Cooper to the top of a hill 7 meters tall. How much GPE does the Mini have at the top of the hill? 2.Ronnie throws a 1-kg football straight up in the air. How much GPE does the football have when it is 9 meters high? 3.Keanna jumps on a trampoline. If she has a mass of 65 kg and jumps 5 meters into the air, how much GPE can she obtain?

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Kinetic Energy Energy of Motion

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Which has more kinetic energy: A falling ping pong ball or A falling bowling ball? Increasing mass increases KE!

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How do you get your bike to go really really fast down a hill? Increasing speed increases KE!

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How much kinetic energy an object has depends on 2 things: Its MASS (kg) and Its VELOCITY (m/s)! KE = ½ * M * V 2 The UNIT for Energy is JOULE (J)!

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EXAMPLE A 3000 kg delivery truck drives down the street at 15 m/s. How much Kinetic Energy does it have? Step 1: Write the given information and the formula M = 3000 kg V = 15 m/s KE = 1/2mv2 Step 2: Substitute the given values into the formula Step 3: Solve the problem (with units!) KE = ½ x 3000kg x (15 m/s)2 KE = ½ x 3000kg x 225 = 337,500 J

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Practice on Your Own 1.Debra pedals her bike at 20 m/s. If she and her bike have a mass of 100 kg, how much KE does she have? 2.A 6-kg alley cat is chasing a mouse at a speed of 4 m/s. How much KE does the cat have? 3.Timara kicks a 1.5-kg soccer ball giving it a velocity of 3 m/s. How much KE does the ball have?

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