an object is dropped from a building 100ft tall. the distance s in feet from the top t seconds later is given by s=16t^2. what is the velocity when it hits the ground?
First solve for t by setting s equal to 100, because that will be the distance from the top of the building when the object hits the ground.
100 = 16t^2
t^2 = 6.25
t = 2.5
Then, since velocity is equal to the change in distance over time, you can divide the change in position (final minus initial, 100 - 0) by the time (above, 2.5 sec) and it will give you your velocity.