# Homework Help: Muscles opperating with efficiency of 18%

1. Oct 9, 2012

### omc1

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. Oct 9, 2012

### 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?

3. Oct 9, 2012

### omc1

i think 2355.10??

4. Oct 9, 2012

### omc1

no wait i got 72716 J....i think thats right then

5. Oct 9, 2012

### omc1

yup that works thanks!