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# Assign6 - PHY 53 Summer 2010 Assignment 6 Reading Energy 2 Key Concepts Potential energy total energy conservation of mechanical energy equilibrium

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Assignment 6 Reading : Energy 2 Key Concepts : Potential energy, total energy, conservation of mechanical energy, equilibrium and turning points. 1. Some statements about the law of conservation of mechanical energy. Comment on their validity and give your reasons. a. The law says that the sum of the kinetic and potential energies of a system remains constant. b. The law says that if the net external force is zero then the sum of the kinetic and potential energies of a system remains constant. c. The law says that if only conservative forces do work then the sum of the kinetic and potential energies of a system remains constant. d. The law says that if all the external forces are conservative then the sum of the kinetic and potential energies of a system remains constant. 2. Some short questions. a. Prove by direct calculation that the work done by a constant force on a particle is independent of the path followed by the particle. b. The static friction force exerted on an object by a stationary surface does no work on the object. Why not? c. When you start your car moving from rest there is an obvious increase in kinetic energy. But the external force (static friction) that causes the acceleration does no work. Does this contradict conservation of energy? Explain.

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## This note was uploaded on 10/19/2011 for the course PHYSICS 53L taught by Professor Mueller during the Spring '07 term at Duke.

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Assign6 - PHY 53 Summer 2010 Assignment 6 Reading Energy 2 Key Concepts Potential energy total energy conservation of mechanical energy equilibrium

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