Consider an imaginary miracle car that has a 100% efficient engine and burns fuel that has an energy content of 40 megajoules per liter. If the air resistance and overall frictional forces on the car traveling at highway speed are 500 N, show that the distance the car could travel per liter

Question

Consider an imaginary miracle car that has a 100% efficient engine and burns fuel that has an energy content of 40 megajoules per liter. If the air resistance and overall frictional forces on the car traveling at highway speed are 500 N, show that the distance the car could travel per liter at this speed is 80 kilometers per liter.

Accepted Answer

From the definition that [latex]work = force imes distance[/latex], simple rearrangement gives distance = work/force If all 40 million J of energy in 1 L were used to do the work of overcoming the air resistance and frictional forces, the distance would be:

[latex]distance = \frac{work}{force} = \frac{40,000,000 J/L}{500 N} = 80,000 m/L = 80 km/L[/latex]

(This is about 190 mpg.) The important point here is that, even with a hypothetically perfect engine, there is an upper limit of fuel economy dictated by the conservation of energy.

Question 5.s&c.7: Consider an imaginary miracle car that has a 100% efficient ...

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