Final answer:
Yes, an object can have zero velocity and nonzero acceleration at a particular instant, such as at the peak of its trajectory when it changes direction, while still being under constant acceleration like gravity.
Step-by-step explanation:
Can an object at one instant of time have zero velocity and nonzero acceleration? The answer is yes. This situation typically occurs at the turning point of an object's motion where it changes direction. For example, when throwing a ball straight up into the air, at its highest point, the velocity will be zero as the ball transitions from moving upwards to falling downwards. However, even at that instant, the ball is subject to gravity, which means it has a constant downward acceleration.
In the context of other questions mentioned, average velocity can indeed be negative if the net displacement is negative, motion can have zero distance but a nonzero displacement and vice versa, and in uniform circular motion, an object is constantly accelerating due to its velocity's changing direction. Additionally, in projectile motion with negligible air resistance, the acceleration due to gravity is never zero, is always in the same direction (downwards), and at times opposite the upward velocity component.