Conservation of energy

# Conservation of - Conservation of energy In the presence of non-conservative forces mechanical energy is converted into internal energy Uint(or

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Conservation of energy In the presence of non-conservative forces, mechanical energy is converted into internal energy U int (or thermal energy): [Delta]U int = - W f With this definition of the internal energy, the work-energy theorem can be rewritten as which is the law of conservation of energy. In words " Energy may be transformed from one kind into another in an isolated system but it can not be created or destroyed; the total energy of a system always remains constant. " Sample Problem 8-8 A ball bearing whose mass is m is fired vertically downward from a height h with an initial velocity v 0 (see Figure 8.4). It buries itself in the sand at a depth d. What average upward resistive force f does the sand exert on the ball as it comes to rest ? Figure 8.4. Sample Problem 5. The work done by the friction force f is given by The initial mechanical energy of the system is given by The final mechanical energy of the system consist only out of the potential energy (K f = 0) E f = U f = m g (- d) = - m g d

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## This document was uploaded on 11/25/2011.

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Conservation of - Conservation of energy In the presence of non-conservative forces mechanical energy is converted into internal energy Uint(or

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