You drop an object. You take the time it takes to hit the ground. So you have Δx (displacement) and time. To find acceleration do you use xf= xi + Vi t + .5at2 Δ x= Vi t + .5at2 Δ x- Vi t=.5at2 a= 2(Δ x- Vit )/ t2 or do you use v= Δ x/ Δ t a= Δ v/ Δ t Should acceleration come out the same? Why do they differ so much? Take example a Δx of 2m and a time of .5. Using the first equation you get 16 m/s^2. But using the second method, you get 8 m/s^2.