Escaping Road Rage

Basic Approach

Use the work/energy method for figuring out the range of a vehicle.
Take the derivative of the range function with respect to velocity, set that equal to zero.
Solve for velocity.


The model I used makes several assumptions.

The second assumption isn't as bad as it sounds. It just means that we might have to drop our results to the upper limit of the engine's horse power.


Let's begin! The force required to keep a vehicle in motion has two parts--aerodynamic resistance and rolling resistance.

F=(1/2)CdAρv2 + μkN

cd - coefficient of drag of vehicle
A - area in the direction of the velocity (frontal area) v - Velocity of vehicle (speed) ρ - density of air (1.225 kg/m3 at sea-lever)
μk - Coefficient of rolling resistance (often assumed to be 0.015 for most vehicles)
N - Normal force (equal to weight of vehicle)

We also know that work is force times a distance.

W = f*d

The ultimate goal here is to be able to drive a greater distance than your pursuer, so we solve the work equation for distance.

d = W/f

We already know the required force, so we can substitute that in!

d = W / [(1/2)CdAρv2 + μkN] ...simplify:

d = 2W / [CdAρv2 + 2μkN]

Excellent! We now have a function that can tell us the distance a vehicle can travel if we know how much work it can do. Conservation of energy tells us that the work is equal to the chemical potential energy of the gasoline. On average, a gallon of gasoline contains 132*106 Joules of energy. To get total work, we just multiply the total gasoline in gallons by 132*106.

Thus, our final equation for the distance a vehicle can travel is:

d = 264*106 / [CdAρv2 + 2μkN]

Next we will need to use some basic calculus to maximize the range difference between the two vehicles.

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