Which quantity is a vector?

• A. Mass
• B. Distance
• C. Displacement
• D. Velocity

Answer: (C)

Vectors are quantities that have both size and direction, while scalars have only size. Displacement fits this idea because it describes how far and in which direction you end up from your starting point, using a specific direction from start to finish. That combination of magnitude and direction makes displacement a vector. Distance, in contrast, is just how much ground was covered without any direction attached, so it’s a scalar. Mass is also a scalar. Velocity is a vector as well, since it tells how fast you’re moving and in what direction (it’s the rate of change of position). So displacement exemplifies the vector nature clearly, even though velocity shares that same property.