Approximately 72 billion liters of milk are produced each year in the United States, from 8 million cows. On average, a single cow consumes 13500 kg of corn feed each year. it required 40 MJ to produce a kilogram of corn feed, which contains 20 MJ of energy. there are 15 MJ of energy in a single liter of milk. Calculate the energy efficiency of growing corn and converting it into milk.

0.25 or 25%

Explanation:

/ represents divided by

* represents multipled by

a Milk in litres 72,000,000,000

b Number of cows 8,000,000

c Milk per cow (litres) 9,000 (a/b)

To calculate how much milk per cow is being produced, you can divide total amount of milk by the number of cows

d Energy Produced Per 1 liter of milk (MJ) 15

e Energy Produced by Each cow (MJ) 135,000 (c*d)

Since we know how much energy is produced by 1 liter of milk, we can calculate total energy produced by a cow on average by multiplying the d and e

f Per cow consumption of corn feed (Kg) 13,500

g Energy used to make 1kg of corn feed (MJ) 40

h Energy consumed by each cow (MJ) 540,000 (f*g)

Since a cow consumes 13500 kg of corn and one kg of corn uses 40MJ of energy, we how much effective energy is consumed by the cow

i Energy Efficiency 0.25 or 25% (e/h)

Since the cow consumed 540,000 MJ to produce 135,000 MJ of energy, we know the energy efficiency is 135,000 divided by 540,000, the efficiency stands at 25%.