Final answer:
The acceleration of an object with constant velocity is zero because there is no change in velocity. Acceleration is a vector quantity that indicates changes in the magnitude and direction of velocity, not the motion itself. So the correct option is d.
Step-by-step explanation:
When considering the acceleration of an object with constant velocity, the correct answer is (d) No acceleration. Acceleration is defined as the rate at which the velocity of an object changes over time. Therefore, if an object is moving at a constant velocity, it means there is no change in its velocity, and thus, the acceleration is zero.
Acceleration can indeed be positive or negative, indicating speeding up or slowing down, respectively. In the context of uniform circular motion, even though the speed of the object is constant, the direction of the velocity is continuously changing, which also constitutes acceleration because acceleration is a vector and considers changes in both the magnitude and direction of velocity.
Additionally, it's important to understand that acceleration and velocity are vector quantities, which means they have both magnitude and direction. A negative acceleration can mean that an object is slowing down, but it could also mean the object is speeding up in the opposite direction of its initial velocity. Meanwhile, a positive acceleration indicates that the object's velocity is increasing in the direction of the acceleration.