The total force required to push a vehicle at speed is the sum of the aerodynamic drag and the rolling resistence. The power required is the total force times the velocity.
FTotal = FDrag + F Rolling Resistence
PTotal = FDragv + F Rolling Resistencev
P = (ref pACdv2)v + r0v
where; FA = Air drag in Newtons, (force)
p = Density of air = 1.23 kg/m3
A = Frontal area in square meters
Cd = Drag coefficient
v = velocity in meters/second
For the GM Impact, power, as a function of velocity, is:
P = ½(1.23 kg/m3)(1.58 m2)(.19)v3 + (9,790 N 0.0048)v
At 60 mph or 100 kph;
P = 4,052.8 + 1,315.8 = 5,368.6 Nm/s = 5.368 Kw
The power require as a function of velocity goes up with the cube of the velocity. This graph illustates this fact for the GM Impact.
The energy consumed for a vehicle to travel is a function of the power being consumed over a period of time or the force over a distance.
Energy = powertime = forcedistence
From the information above, the GM Impact require 5.368 kilowatts at 97 kph (60 mph). In one hour the Impact would consume 5.368 kilowatthours, kwh. Also, the Impact requires a force of 193.65 Newtons to travel at 97 kph. In one hour the vehicle will travel 97 km. The energy consumed is 97,000m193.65N = 18,784,050 Nm or 5.218 kwh. So, whether the energy is determined by power and time or force and distence, the results can be very close.