1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Energy from a Fast Food Meal

  1. Dec 4, 2009 #1
    1. The problem statement, all variables and given/known data

    For how long would a 68 kg person have to swim at a fast crawl to use all the energy available in a typical fast food meal of burger, fries, and a drink? Assume 25% efficiency.

    2. Relevant equations

    Fast food meal provides 1350 Cal or 5670 kJ
    A 68 kg person swimming at a fast crawl uses 800 W of metabolic power.

    3. The attempt at a solution

    I'm having trouble just setting up the equation.
    I know that Change in Thermal Energy + Change in Chemical Energy = 0 because it is an isolated system, but I don't know where to go from here, nor do I know what units I need each part to be in.
     
  2. jcsd
  3. Dec 4, 2009 #2

    Pengwuino

    User Avatar
    Gold Member

    Well, just think about this question for a second. This person intakes a certain amount of energy by eating the food. 25% of that energy is useable. The person then performs some activity that takes a certain amount of energy per second (or 800 J per second). You should be able to determine how long the person can swim just by giving the question some thought.
     
  4. Dec 4, 2009 #3
    So would it be 5670*.25=800W* time?

    Solving for time gives me 1.77 - but what units is this?
     
  5. Dec 4, 2009 #4
    Op never mind, I needed to change kJ into Joules, then it gives me time in seconds. Whoops. :D
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Energy from a Fast Food Meal
Loading...