Apiston in a heat engine does 600 joules of work and 1,700 joules of heat are added to the system. determine the change in internal energy and explain how this example demonstrates the conservation of energy.

The change in internal energy is calculated by obtaining the difference between the heat and the work. That is,
                       change in internal energy = 1,700 J - 600 J
                                                                       = 1,100 J
This is an example of conservation of energy because the energy that is not used for the worked performed is converted to internal energy. 

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Answer(a)   the matererials that are in contact, the two materials and the nature of their surfaces/// (b)/// the force pushing the two surfaces together, pushing the surfaces together causes the more of the asperities to come together and increases the surface area in contact with each other