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Homework Help: Muscles opperating with efficiency of 18%

  1. Oct 9, 2012 #1
    1. The problem statement, all variables and given/known data Muscles operate with an efficiency of about 18.0 percent in converting stored chemical energy into work. How much chemical energy will be expended by a 63.6 kg person in the process of ascending several flights of stairs to a height of 21.0m?

    2. Relevant equations pe= mgh(initial)

    3. The attempt at a solution pe=13088.88 J i wasnt sure if the 18% had anything to do with the problem or not
  2. jcsd
  3. Oct 9, 2012 #2


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    2017 Award

    Staff: Mentor

    The 18% are relevant.

    13088.88 J is the potential energy the person gains. However, the question asks for the chemical energy.

    Muscles can convert this chemical energy into work with 18% efficiency - if you expend 100 J of chemical energy, you can gain 18 J of potential energy (at least according to this problem). How much chemical energy to you need to gain 13088.88 J of potential energy?
  4. Oct 9, 2012 #3
    i think 2355.10??
  5. Oct 9, 2012 #4
    no wait i got 72716 J....i think thats right then
  6. Oct 9, 2012 #5
    yup that works thanks!
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