The Weight Watcher And His French Fries
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The Weight Watcher And His French Fries

A 200 lb man decides to add to his exercise routine by walking up three flights of stairs (45 ft) 20 times per day. He figures that the work required to increase his potential energy in this way will permit him to eat an extra order of french fries, at 245 Calories, without adding to his weight. Is he correct in this assumption?

The strings: S7P3A31 (force - pull).

The math:
Pj Problem of Interest is of type force (pull). This is work that is a consequence of the pull of gravity.

200 lb = 200 x 0.447 = 89.4 kg.
So, mass of man = 89.4 kg
Acceleration due to gravity, g = 9.80 m/s2
Distance = 45 ft = 45/3.28 = 13.72 meters
Potential energy = mgh = 89.4 x 9.80 x 13.72 = 12020 J = 12.020 kJ
For 20 times per day = 12.020 x 20 =240.4 kJ
1 kcal = 4.184 kJ = 1 Cal
So, 240.4 kJ = 240.4/4.184 = 57.46 Cal.
So, energy expended to climb stairs = 57.46 Cal, if all work is used to increase potential energy.
So, the stair climbing exercise will not compensate for the extra order of 245 Cal fries.
In actuality more than 58 Cal will required to climb the stairs because of the energy needed to move the limbs and the energy lost as heat.

Blessed are they that have not seen, and yet have believed. John 20:29