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Answer:
D. Acceleration is always in the same direction as velocity.
Explanation:
First of all, let's remind the definition of acceleration:
Acceleration is equal to the rate of change in velocity, in formula
where is the change in velocity and
is the time interval.
It is important to keep in mind that acceleration is a vector, so it has a direction.
Now let's analyze each statement:
A. Acceleration can be zero, positive, or negative. --> TRUE. When acceleration is positive, it means that its direction is the same as the velocity, so the object is speeding up; when acceleration is negative, it means that its direction is opposite to the velocity, so the object is slowing down; when acceleration is zero, the object has constant velocity.
B. An object can have acceleration with zero velocity. --> TRUE. In fact, an object can be moving with a positive velocity and having a constant negative acceleration: this means that its velocity will decreases until it becomes zero and then it turns negative. At the moment the velocity is zero, the acceleration is not zero.
C. An object can have acceleration with negative velocity. --> TRUE. The direction of the acceleration does not depend on the direction of the velocity: an object with negative velocity is moving in the direction opposite to that used as reference, so it can still have an acceleration.
D. Acceleration is always in the same direction as velocity. --> FALSE. As we we said in point a and c, the direction of the acceleration does not depend on the direction of the velocity, so an object with positive velocity, for example, can have a negative acceleration (it means that the acceleration is in the opposite direction, so the object is slowing down).