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To figure out how many calories you burned,
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we're going to need to solve for how much work you do
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and we know from the work energy theorem that the work you do
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is equal to the change in energy of the weight.and the changed energy of the weight
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is equal to the change in it's kinetic energy plus the change in it's potential energy.
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Well the weight starts at rest and it ends at rest too, so the change in kinetic energy is zero.
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But it does change in potential energy when you raise it at 1 m.
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Okay, so using energy (mg)h for the potential energy of the weight
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and plugging in all my numbers, I do a little math and I get that each time I raise the weight,
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I need to do 100 joules of work but that's just for one raising of the weight.
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How much work do I have to do to raise it over my 4-minute workout.
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I chose to do this next part of the problem using conversion factors.
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The workout takes 4 minutes and there are 60 seconds in 1 minute,
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so these minutes are cancelled and we do 2/3 repetitions per second,
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so the seconds are cancelled, and we do 100 joules of work for each repetition,
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so repetitions are cancelled and there's 1 calorie per 4200 joules, so joules are cancelled.
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Okay, now let's multiply all these numbers together and we get that
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over the course of our 4-minute workout, we burned 7.62 calories. Great work.