Posted by RANDY on .
how do we derive the formula at=vfvi if we will find acceleration? please have it step by step. Thank you

SCIENCE 
Steve,
we do it the same way we figure the average speed. Divide the distance covered (∆s) by the time taken (∆t).
For acceleration, it's the same. The average acceleration is the change in speed (∆v = vfvi) by the amount of time it takes to make the change (∆t).
a = ∆v/∆t
a*∆t = ∆v
if we start at t=0, then ∆t = t, the time taken:
at = ∆v = vfvi
or, think about what constant acceleration means. Each second, the velocity changes by a fixed amount (the acceleration). So, after t seconds, the velocity has changed by at. But the amount changed is ∆v = vfvi. SO,
at = vfvi