Question from my Kinematics Exam.

[x2468]

okay this is really retarded. but i actually got stuck on this question today. i think it went something like:
a car accelerated from rest and traveled 81 meters in 9 seconds. what was its acceleration?
it was like the simplest Q on the exam. but i cept thinking it must be 9m/s/s because in the first second its going 9, then 18, so on and so on to 81 meters in 9 seconds? but i did the math and got 2 m/s/s. I am still not totally sure. 9 and 2 were both choices. i went with 2. right chocie or wrong?
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upon writing this, i think i simply got m/s mixed up with m/s/s

 

[kp]

a = 2d/t^2

a= 2m/s/s

9m/s/s is really fast, like crotch rocket fast

 

[Cyrus]

$$y=y_0+v_0t+ \frac{at^2}{2}$$

$$81.0= 0+ 0+ \frac{a(9)^2}{2}$$

so a= 2,

you got it right. (I assumed constant acceleration).