An important task in everyday life is the pumping of water from underground wells. Among other methods, this can be carried out either by human effort or by a machine. We wish to compare the energy costs of these two methods of pumping 10,000 kg from a depth of 100 m. Assume that a person is fed with eggs. An egg provides 80 kcal of energy and costs about 10 cents. the human body transforms caloric food into muscle power with an efficiency of about 25%. A gasoline engine transforms fuel into a motive power with an efficiency of about 25%. Gasoline has a density of about 750 kg/m3 , can make available about 40,000 kJ/kg, and is priced at about $3.00 per gallon in most places except the United States.
(a) Find the energy cost of each of these two methods of pumping the water.
(b) By considering other foodstuffs and including in your approximate calculations both capital and labor costs, which of the two ways of pumping water would you recommend? Express your considerations and recommendations in a paragraph or so.
