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Calories Needed

  1. Oct 23, 2008 #1
    1. The problem statement, all variables and given/known data
    On a typical stage the riders conserve energy by staying in the pelaton. This greatly reduces aerodynamic drag on all riders except the ones at the front. Pelaton riding requires only about 60% of the power of needed for a time trial. Suppose a typical pelaton rider's power output averages 250 watts for a 5 hour stage. The human body is about 25% efficient at converting chemical energy from food into work. Estimate the total daily Calorie input from food needed for a Tour rider to maintain weight.

    2. Relevant equations
    In a previous problem it told us that a normal person Basal Metabolic Rate is 100 watts. So that would be then 100J/s and 360000J/hr. There are 4180J per kcal or calorie. now what i am having a problem with is that when i go to find the ammount of calories i come up with only 2710.55 calories by doing 250w=250J/s=900000J/hr so while they are biking they are losing 215.31 kcal per hour or a total of 1076.55 kcal in the 5 hour bike ride. Then i just figured out the amount of calories burned at a normal persons BMR and added them giving me the total i had stated before of 2710.55 which does not sound like enough to me and i wanted to make sure that i am actually doing it right. i checked online and it said that the people while doing a bike race can consume between 8000 and 10000 kcal per day just to keep at weight so i am guessing i messed up somewhere. I am not sure who the % come in and help with this equation.
  2. jcsd
  3. Oct 23, 2008 #2


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    Are you properly accounting for the 25% efficiency of chemical to mechanical?
  4. Oct 23, 2008 #3
    no that is the problem that i am having. i am not sure how to use the %'s they give at all. like i dont know when or how or why to use them
  5. Oct 23, 2008 #4


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    Certainly it should apply at least to the mechanical energy requirements as they are in addition to the basal requirement. Since the Basal amount is already somewhat given, then I'd say you would apply it to the 215 cal/hour or 860 cal/hour or over 5 hours an additional 4300 + the 2700 basal = 7000.
  6. Oct 23, 2008 #5
    ok that makes so much more sense. there is actually another problem that i was having trouble on, i will post it in a sec so if you could help with that, then that would be awesome
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