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!

Joules and mass

  1. Apr 5, 2010 #1
    1. The problem statement, all variables and given/known data
    Consider two friends who go to Burger King every day for lunch. One of them orders a double whopper sandwich large fries and a large coke (total cal = 1600) while the other orders a whopper junior small fries and a small coke every day (cal = 800).
    if these two friends are very similar otherwise and they have the same metabolic rate, determine the weight difference between these two friends in a year.

    2. Relevant equations
    I know of know no other equation that relates energy to mass besides this one.
    Does it apply here?
  2. jcsd
  3. Apr 5, 2010 #2
    haha ive never heard of such a question. one calorie is 4.184 joules according to google. thats oddly close to the specific heat capacity of water, off topic sorry.

    and yeah thats what I would do. what are you studying right now in physics, relativity? energy?
  4. Apr 5, 2010 #3
    however, that cannot be right. c^2 is like 9e18...which would mean you could eat like thousands of trillions of calories more and not even gain a kilogram.
  5. Apr 5, 2010 #4
    sorry for the multiple posts, I just found this little statistic here on yahoo answers

    7709 cal = 1 Kg
  6. Apr 5, 2010 #5
    One calorie here is actually one Kcal and thus 4.184 kilo joules. The "kilo" is omitted by the food industry and dieticians.

    Hint: What is the energy content of one kg of fat?
  7. Apr 5, 2010 #6
    Yes, that looks plausible, A rule of thumb is that 4 days of fasting will lead to about 1 kg of weight loss. We use about 2000 kcal of energy per day, but if you don't eat, then it will be a bit less.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook