Abullet with mass 1.0kg and velocity 180 m/s is brought to rest in 0.02 s by a sandbag. assuming constant acceleration in the sandbag, how deep, in meters, did the bullet penetrate the sandbag

Hello
The bullet is moving by uniformly accelerated motion.
The initial velocity is , the final velocity is , and the total time of the motion is , so the acceleration is given by
 
where the negative sign means that is a deceleration.
Therefore we can calculate the total distance covered by the bullet in its motion using

So, the bullet penetrates the sandbag 1.8 meters.

Is a  vector quantity  that refers to "the rate at which an object changes its position." imagine a person moving rapidly - one step forward and one step back - always returning to the original starting position. while this might result in a frenzy of activity, it would result in a zero velocity. because the person always returns to the original position, the motion would never result in a change in position. since velocity is defined as the rate at which the position changes, this motion results in zero velocity. if a person in motion wishes to maximize their velocity, then that person must make every effort to maximize the amount that they are displaced from their original position. every step must go into moving that person further from where he or she started. for certain, the person should never change directions and begin to return to the starting position.