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Lec15 - Lecture 15 Mon 28 Sept 09 Chapter 7 Potential...

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Lecture 15 Mon 28 Sept 09 Chapter 7: Potential Energy and Energy Conservation Reformulate the Work-Energy Theorem Three definitions of a conservative force -- Gravitational and spring forces are conservative -- Friction forces are not conservative • A potential energy U is a function of position of a particle that is associated with a conservative force • The mechanical energy E = K + U of a particle is the sum of its kinetic and potential energies at each position If no nonconservative forces act on a particle, the E of the particle does not change with time ( E is conserved), which is the principle of conservation of mechanical energy
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Structure of Classical Mechanics: Part 2 Scalar Theory of Motion: Reformulate the Work-Energy Theorem
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The change in the gravitational potential energy of the ball is __ J. 1. 80 2. ± 80 3. 40 4. ± 40 Question A 0.20 kg ball is thrown straight up with an initial speed of 20 m/s and then momentarily comes to a stop at the top of its trajectory. Given: m = 0.20 kg, v 1 = 20 m/s, v 2 = 0. Use conservation of mechanical energy: ± U = ²± K = ²
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