Final answer:
The acceleration of an object is zero when the net force acting upon it is zero. This follows from Newton's second law, meaning the object is either stationary or moving with a constant velocity.
Step-by-step explanation:
Whenever the net force on an object is zero, its acceleration is zero as well. This conclusion is directly derived from Newton's second law of motion, which states that the acceleration of an object is directly proportional to the net force acting upon it and inversely proportional to its mass (F=ma). Thus, if the net force is zero, the acceleration must also be zero, regardless of the mass of the object. This implies that the object could either be at rest or moving at a constant velocity, as there is no unbalanced force to change its state of motion.
For instance, when a car moves with constant velocity, the net force on the car is balanced. Frictional forces balance out the drag forces, leading to a net force of zero. Similarly, when a car is parked, all forces are balanced, and both the net force and acceleration are zero. Therefore, when the net force is zero, the correct answer is A) Is zero, meaning the acceleration is zero.