Understanding the Concepts

* Acceleration: The rate at which an object's velocity changes. It's measured in meters per second squared (m/s²).

* Initial Velocity (vi): The object's starting speed (9 m/s).

* Final Velocity (vf): The object's ending speed (0 m/s since it comes to a stop).

* Time (t): The time it takes for the object to slow down (3 s).

Formula

The formula for acceleration is:

acceleration (a) = (final velocity (vf) - initial velocity (vi)) / time (t)

Calculation

1. Plug in the values:

a = (0 m/s - 9 m/s) / 3 s

2. Simplify:

a = -9 m/s / 3 s

3. Calculate:

a = -3 m/s²

Answer

The object's acceleration is -3 m/s². The negative sign indicates that the acceleration is in the opposite direction of the object's initial motion, meaning it's slowing down (decelerating).