## Environmental Science for AP* (2nd Edition)

We know how much energy a car uses per kilometer, and we want to find how much energy a car uses per person. We will be using dimensional analysis as well. Let's first determine how much energy is required to drive 1-mile using dimensional analysis, since the length of the car trip is in miles and not kilometers. We know that one mile is about 1.61 kilometers: $\frac{3.6 MJ}{1 km} * \frac{1.61 km}{1 mile} = \approx \frac{5.8 MJ}{1 mile}$ Now let's find the number total amount of energy needed to drive the 400-mile trip: $\frac{5.8 MJ}{1 mile} * 400 miles = 2,320 MJ$ Now let's find the amount of energy needed per person: $\frac{2,320 MJ}{4} = 580 MJ$