Displacement is a vector. It has magnitude and direction. The direction is dependent on the direction of the object’s initial velocity. In the example below, a ball is thrown upward. This is the positive direction. Since it accelerating toward the street, the acceleration is negative.
Displacement = final position – initial position
One of the most common examples is when an object is on top of building. For example, the building is 30 meters tall. A ball is thrown upward at 20 m/s. Let’s use the following equation to determine the ball’s velocity just before it hits the street.
vf^2 = vi^2 + 2 * a * d. a = -9.8 m/s^2, d - -30 meters
vf^2 = 20^2 + 2 * -9.8 * -30
vf = ± √988
This is approximately 31.4 m/s. Since the ball is moving downward, its velocity is negative. Let’s use the following equation to determine the time.
vf -= vi + a * t, a - -9.8 m/s^2
-√988 = 20 – 9.8 * t
t = (-√988 + -20) ÷ 9.8
This is approximately 5.25 seconds. I hope this is helpful for you.