Question

Ill give a medal and fan to anyone who can just do this for me. I seriously did terrible in the module and don't understand that question.
What is the energy efficiency of a car that has 100% useable gasoline that is extracted from an oil well at 60% efficiency, transported via ship at a 90% efficiency, refined at a 75% efficiency, transported via truck to the gas station at a 84% efficiency, and burned by your car at a 65% efficiency?

Answer 1

Look at it this way. You take 100 gallons of oil out of the ground, but it take 40 gallons of the oil to run the pumps. So we say the oil is extracted at 60% efficiency, 100 gallons times 0.6 = 60 gallons of oil to sent to the ship.

Out of that 60 gallons of oil on the ship, the ship uses 10% or 6 gallons of oil. So 60 gallons times 0.9 = 54 gallons. So there is now only 54 gallons goes to the refinery.

Out of the 54 gallons, the refinery is able to convert only 75% of the oil to gas. So 54 gallons times .75 = 40.5 gallons of gas sent to the truck.

Out of the 40.5 gallons the truck uses 16% of the gas or the 6.48 gallons. This leaves 84% of the gas for the car. So 40.5 gallons times .84 = 34.02 gallons of gas.

Out the 34.02 gallons of gas the car uses 65% of the gas to move the car. The rest is wasted. So 34.02 gallons times .65= 22.113 gallons

So out of the 100 gallons only 22.113 gallons moves the car.

So the efficiency is 22.113 divided by 100 or 22.113%