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April 7, 2009 • Study for 5 min for your quiz. • You need: Calculator and Writing Utensil • When you are done with quiz: Bring it up and pick up a note sheet for Energy! Goals • To explain different types of energy • To calculate potential and kinetic energy Q: What is ENERGY? • Energy is…. – the ability to do work – a measure of how much work is done – a word to describe the power and effort of a force. – measured in Joules ENERGY • Energy is the ability to do work • Doing work uses energy • An object can gain energy if work is done on it Q: What is ENERGY? • Two MAIN types of mechanical energy: – Potential energy – Kinetic Energy Q: What is POTENTIAL ENERGY? Potential Energy (PE) is stored energy • Coaster has PE when it is at the top of the hill. Even if it isn’t moving yet, it may if a force is applied and it begins to move Q: What is POTENTIAL ENERGY? • Gravitational potential energy (GPE) is the energy of an object due to its position above the surface • GPE = mgh = wh • m=mass (in Kg) • g=acceleration due to gravity … 9.8 m/s2 • h= height (in m) • w = weight (N) • UNITS: “Homework” • Complete the Practice Problem for PE on your note sheet! PRACTICE PROBLEM: Find the PE of a rock climber as she climbs 35 m above the base of a cliff. Her mass is 65 kg. • Given: h = 35 m m = 65 kg g = 9.8 m/s2 GPE = ? • Equation: GPE = m x g x h • Solve: GPE = 65 kg x 9.8 m/s2 x 35m =22,295 J Q: What is KINETIC ENERGY? • Kinetic Energy (KE) is the energy due to an object’s motion – Active energy – A rock as it falls off of a cliff • Formula: KE = ½ * m * v2 – m= mass (kg) – v = velocity (m/s) • UNITS: PRACTICE PROBLEM: What is the KE of a 44 kg Cheetah running at 31 m/s? • Given: – m = 44 kg – v = 31 m/s – KE = ? • Equation: KE = ½ * m * v2 •Solve: KE = (1/2) (44 kg) (31 m/s)2 21,142 J Homework • Kinetic and Potential Energy WS