physics question - in order to lift a 50 kg height from the ground to over your head, a vertical distance of 2.2 m how much metabolic energy must

Question

in order to lift a 50 kg height from the ground to over your head, a vertical distance of 2.2 m how much metabolic energy must be expended assume the usual efficiency for the human body of 25%.

Answer 1

Hi James,

By lifting the 50 kg body to the height of 2.2 m you increased its energy by 50 kg x 2.2 m x 9.8 m s^-2 = 1,078 J

This energy “came” from somewhere, namely from the metabolic energy expended by you. Since your efficiency is 25% (which is the same as 1/4), the energy you expended was 4 x 1,078 J = 4,312 J

Interestingly, this is very close to 1 kcal which lay people usually refer to as simply a calorie. Which is to say that in theory to replenish the expended energy you need to consume about 0.25 g of sugar.