How is velocity defined?

Velocity is defined as the speed of an object in a given direction. It's a vector quantity, which means that it not only measures how fast an object is moving but also specifies the direction in which the object is moving. For example, saying a car is traveling north at 60 kilometers per hour gives both its speed and direction, which is essential for a complete understanding of its motion.

In contrast, other definitions provided in the options do not capture this essential aspect of direction. The distance traveled relates only to how much ground an object covers and does not take direction into account. The mass of an object over time doesn't adequately describe motion at all, as mass is a scalar quantity independent of how fast or in what direction something is moving. Lastly, the rate of change of velocity refers to acceleration, which is a different concept altogether, involving the change in velocity over time rather than defining velocity itself.