This is for personal study and as I am on study leave its a bit hard to contact a teacher.
This is the question; (the circled answer was the teachers answer)
I'm unsure as to why you would individually square the times before subtracting as the actual time is (t2-t1) substituted into time on the equation, squaring before will result in a larger value (small value for acceleration though). It is possible the teacher merely got it wrong (has been known to happen).
s=ut + (1/2)at^2
The Attempt at a Solution