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Lost Energy? The principle of the conservation of energy
Chapter 7, Problem 6DQ(choose chapter or problem)
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?
Questions & Answers
QUESTION:
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?
ANSWER:
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.