To find the acceleration, we first need to know the time it took to travel the 0.35km. We can find the time knowing that the distance for uniformly accelerating motion can be found by multiplying the average velocity by the time it took to cover the distance.
d = (1/2)(vf + vi)(t)
0.35km = (0.5)(40m/s +10m/s)(t)
350m = (25m/s)(t) => 14s = t
So acceleration = (40m/s - 10m/s) / 14s
Giving us our acceleration: ~ 2.143 m/s2
