Joules and mass

Ry122

Homework Statement

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.

Homework Equations

I know of know no other equation that relates energy to mass besides this one.
Does it apply here?
E=mc^2

dacruick
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?

dacruick
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.

dacruick
sorry for the multiple posts, I just found this little statistic here on yahoo answers

7709 cal = 1 Kg

Count Iblis
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?

Count Iblis
sorry for the multiple posts, I just found this little statistic here on yahoo answers

7709 cal = 1 Kg

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.