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What is the energy of a ball lying on the ground at rest? As it is not in motion, it will have zero kinetic energy and as it is lying on the ground its potential energy will also be zero, taking the zero potential energy at the ground.

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First of all, you need to be specific of which energy you are looking for.

The phrase "the energy" is not specific as people may interpret it in different ways based on their common practices. If you define your zero valued potential energy at the ground, then the mechanical energy is zero.

Note that if the mechanical energy is zero, it does not mean that "the" energy is zero. If you define your ball as the system, there may be an "exchange" of thermal energy between the ball (the system) and every thing else (the surroundings).

Well, for simplicity, we would first assume that the system is isolated and therefore no thermal energy is being added/removed to/from the system, then we can say that "the" energy of the "system" is zero.

Also, there are other forms of energy but I assume their values are zero, too.

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If the questions says that zero potential energy level is on ground then the answer is zero for total mechanical energy. but in actual the zero potential energy level is at infinity. You will define a different point for Z.P.E.L only while doing a calculation with mechanical energy to do it easily.

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