I have an exercise with a pendulum starting at horizontal position, then we give it a velocity of 5m/s pointing down, $z=0$ at this horizontal position and potential energy = 0. This confuses me because then if we dont't have that initial velocity the mecanichal energy at start would be 0, but still the pendulum have mecanic energy (if we let it down it will swing). Is the exercise statement wrong?
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1$\begingroup$ What is the problem with kinetic energy being able to go positive because the potential energy can go negative? It is perfectly fine for mechanical energy to be zero, or negative, and yet have things move. Nothing is wrong here. $\endgroup$– naturallyInconsistentCommented Feb 18 at 11:31
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$\begingroup$ ok but then it will be hard to find questions like maximal height, if we apply conservation of mechanical energy at maximal height all the kinetic energy is turned into potential energy but then we have both of them initially null so how to proceed $\endgroup$– dddr rdddCommented Feb 18 at 11:36
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$\begingroup$ No, it is not going to be difficult. There is a minimum of the potential energy, in this case being some size of negative number, and that size of energy will then be the kinetic energy; Similarly, the kinetic energy has a minimum of zero, and when that happens, you can find the maximum of the potential energy, which will determine the maximal height. You are just not familiar with this, it is not difficult. $\endgroup$– naturallyInconsistentCommented Feb 18 at 11:43
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$\begingroup$ thanks for clarifying $\endgroup$– dddr rdddCommented Feb 18 at 13:40
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