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# How many times more chemical energy does a car have to expend to reach 100km/h instead of 50 km/h?

### 3 Answers

- Anonymous1 decade agoFavorite Answer
Doubling the speed of something requires four times as much energy.

This is because KE = 1/2(m*v^2)

- Anonymous1 decade ago
The above answers would be correct if air flow were laminar around the vehicle, i.e., no turbulence. At higher speeds, turbulent flow makes the air drag proportional to the square of velocity, so the power is then proprotional to the cube of velocity.

Wikipedia just happens to have this exact problem worked out for you. It says a car at 50 mph might require 10 hp and at 100 mph, 80 hp. However, different vehicles make the transition from laminar to turbulent flow at different speeds, depending on the shape of the chasis; so the right answer might lie somewhere between 4x and 8x power consumption.

But that is only the work against the air drag. Fuel consumption would depend on the engine. Different engines have different efficiency curves. Most auto engines have max efficiency near 50 mph; at 100 they consume more fuel per horsepower. A race car, designed to average 200 mph would be less efficient at 50 mph.

Source(s): http://en.wikipedia.org/wiki/Drag_(physics) - 1 decade ago
As a minimum, four times as much, because of the basic calculation of kinetic energy already mentioned in the other answers. In practice, more than that because of air resistance and tire losses, which are dependant on the details of the design.