Explain why an object can move at a constant velocity when the resultant force acting on it is zero.

An object can move at a constant velocity when the resultant force is zero because the forces acting on it are balanced. This means that the forward forces are equal to the backward forces, resulting in no change in motion, allowing the object to maintain its speed and direction.

This question assesses the student's ability to connect the concept of balanced forces with uniform motion. The answer reflects an understanding of Newton's first law of motion, which states that an object will remain at rest or in uniform motion unless acted upon by a net external force.