Which statement is true about velocity and speed?

• A. Velocity is a scalar and speed is a vector.
• B. Velocity is speed with a direction; speed is just magnitude.
• C. Speed is a vector quantity.
• D. Velocity has no magnitude.

Answer: (B)

Understanding the difference between speed and velocity is key: speed is how fast something is moving, without regard to direction, so it’s a scalar quantity. Velocity, on the other hand, includes both how fast and in which direction, making it a vector quantity.

Think of moving at 20 meters per second toward the east. That describes speed (20 m/s) and velocity (20 m/s east) together—the speed is the magnitude, the velocity adds the direction. Because velocity has direction, it’s possible for speed to stay the same while velocity changes if the direction changes, such as in circular motion; the object isn’t speeding up or slowing down, but its velocity is continually changing due to the changing direction, which is a form of acceleration.

So the true statement is that velocity is speed with a direction, while speed is just the magnitude. The other ideas aren’t correct because velocity is not a scalar, speed isn’t a vector, and velocity does have magnitude.