How can you derive v equals u plus at?

Answer 1

You mean the formula v = u + at, where v is final velocity, u is starting velocity, a is the rate of acceleration and t is the time taken.

Well if a car's acceleration is 20 feet per second per second, in 12 seconds its velocity will have been increased to 20 x 12 = 240 feet per second.

So if before it accelerated it was travelling at 100 feet per second, its new speed will be 240 + 100 = 340 feet per second = 340 x 60 x 60 ft per hour = 1224000 ft/hr

which is just under 219 mph! Some car!