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← 06ps-06 Weight Lifting Solution

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Showing Revision 1 created 10/27/2012 by Amara Bot.

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