A car goes from 40m/s to 80 m/s in a distance of 200m. What is its average acceleration?

Answer 1

a = (v1^2-v0^2)/(2x) = 12 m/s^2
See the ref. for derivation, or:
Note that the average velocity = (40+80)/2 = 60 m/s
Then the car covers the distance in 200/60 = 3.333 s
Its acceleration is (80-40)/3.333 = 12 m/s^2

Answer 2

a=dv/dt and v=dx/dt

ergo . . .
a = vdv/dx

v=40
dv = 80-40 = 40
dx = 200

a = 40(40)/200=8m/s^2

Answer 3

50-60 mls