On a straight road (taken to be in the + x direction) you drive for an hour at 40 km per hour, then quickly speed up to 110 km per hour and drive for an additional two hours. how far do you go ( delta x)? total distance = km what is your average x component of velocity (v avg, x) v avg, x = km/hr why isn't v avg, x equal to the arithmetic average of your initial and final values of v x, (40 + 110)/2 = 75 km per hour? the velocity isn't constant. the arithmetic mean is not a valid way to calculate the average in this situation. the initial velocity isn't zero.