## Energy and Calories

A man (90 kg) climbs up a ladder 30 meters high. The energy he has due to his position can be calculated.

Potential Energy = mgh

PE = 90kg * 10m/s2 * 30m

PE = 27000kg m2/s2

PE = 27000 Joules

 m = mass of the man g = acceleration due to gravity h = position of man after climbing the ladder Joules = unit for work or energy

Energy can be converted to heat or calories.

4.2 Joules = 1 calory

1 calory is the amount of heat needed to raise 1 gram of water by 1oC. The calories in food are kilocalories or thousand calories.

When the man's potential energy is converted to calories, it becomes :

Potential Energy = 6400 cal

PE = 6.4 Kcal

Suppose the man ate a packet of chips which is about 2000 Calories. (Notice the capital c for Calories. If calories is written with a capital c, then it is equal to kilocalories.)
He would have to climb up and down 30 meter high ladder about 150 times to get rid of what he ate.
Of course this figure is disregarding the energy needed to maintain himself.