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Introductory Physics Homework Help
About work done through exercise (push ups)
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[QUOTE="PeroK, post: 6566560, member: 493650"] This is a poor question, because biomechanics is generally more complicated than elementary physics, owing to the way the muscles work. The woman would get tired simply remaining in the "plank" position at the top of a press-up, without moving at all. The question would do better to ask you to analyse the work done on an object as you raise and lower it. The human body is generally very inefficient, so the external work done is often much less than the energy expended (I'm not even sure that's a well-defined term, but let's assume it's how much energy is produced by her muscles). That's the elementary calculation all right. To do a press-up requires the woman to do about ##98J## work on her own body mass. On the way down, or when you lower an object, you must do negative work on the object. In other words, your muscles must absorb the energy in some way. This energy doesn't get stored like in a spring, but rather gets dissipated as heat in your muscles. Again, biomechanics is quite complicated. Energy is a scalar quantity, but work is a [I]scalar product[/I] (of two vectors), which can be negative or positive. The work done overall by a press-up and down is, indeed, zero. In an idealised scenario, the energy would start stored as chemical energy in your muscles and end as heat in your muscles. That's approximately the effect of doing press-ups! This is why your muscles tire, even though you are doing zero work overall: you are expended the chemical energy in your muscles which must eventually be replaced. [/QUOTE]
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About work done through exercise (push ups)
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