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Lost Energy The principle of the conservation of energy

University Physics | 13th Edition | ISBN: 9780321675460 | Authors: Hugh D. Young, Roger A. Freedman ISBN: 9780321675460 31

Solution for problem 6DQ Chapter 7

University Physics | 13th Edition

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University Physics | 13th Edition | ISBN: 9780321675460 | Authors: Hugh D. Young, Roger A. Freedman

University Physics | 13th Edition

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Problem 6DQ

Lost Energy? The principle of the conservation of energy tells us that energy is never lost, but only changes from one form to another. Yet in many ordinary situations, energy may appear to be lost. In each case, explain what happens to the “lost” energy. (a) A box sliding on the floor comes to a halt due to friction. How did friction take away its kinetic energy, and what happened to that energy? (b) A car stops when you apply the brakes. What happened to its kinetic energy? (c) Air resistance uses up some of the original gravitational potential energy of a falling object. What type of energy did the “lost” potential energy become? (d) When a returning space shuttle touches down on the run way, it has lost almost all its kinetic energy and gravitational potential energy. Where did all that energy go?

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Solution 6DQ Yes energy can never be lost. The conservation of energy tells that, the total amount of energy of this whole universe is just a number which we don’t know. What we know is, that number never changes which is a constant. When you add up all the forms of the energies, the number will be invariant. a)A box sliding on the floor comes to a halt due to friction. We know that friction is not a conservative force and the energy dissipates to the surrounding by it, for which the total energy of the system does not remain the same as before. It does not mean that energy conservation is wrong. The friction causes heat to generate which adds up to the energy of the surrounding. When you consider this heat energy released during the motion, you will get the exact number which was before. Hence energy conservation is saved. b)When a car is moving, it can be stopped by the brakes. The kinetic energy of the car will be lost. But it would increase the heat energy created by the friction between the wheels and the brake. Again when you add up this heat, the total energy you will observe as unchanged. c)When an object falls freely under gravity, the final kinetic energy just before hitting the ground would not be equal to the initial gravitational...

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Chapter 7, Problem 6DQ is Solved
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Textbook: University Physics
Edition: 13
Author: Hugh D. Young, Roger A. Freedman
ISBN: 9780321675460

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Lost Energy The principle of the conservation of energy

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