Final answer:
A system can have a nonzero velocity with zero net external force as per Newton's first law of motion, which is evident in a car cruising at a constant velocity on a highway when forces are balanced.
Step-by-step explanation:
A system can indeed have a nonzero velocity while the net external force on it is zero. This situation is described by Newtons first law of motion, which states that an object in motion will stay in motion with a constant velocity unless acted upon by a net external force (also known as inertia).
A classic example of this is when a car is cruising at a constant velocity on a highway. If there is no acceleration or deceleration, the forces such as the engine's thrust and air resistance are balanced, leading to a net external force of zero. Hence, the car continues to move at a constant velocity due to its inertia.