We are in the annual solar race in Australia and have gone 500 Km but its been cloudy so the poor solar powered racer can only manage 50 KM/hr for the first 500 Km. Then at that point, the clouds go away and the little racer can get to its top speed of 80 Km/hr. Assuming no accel time, just a jump function to make it simpler, how many Km/hr per km does the total average go up? For instance, one klick past the 500 klick mark the car has just done that one click at 80, how much has the average for the 501 Klicks gone up, then the next klick, etc. Is this a linear curve? Power curve? What is the function of the change in average velocity say summing it up for the next 500 Km where the vehicle goes 80 klicks the whole second part.