Answer: d) Position vector
Velocity = Speed = constant
As the position of particle changes with time so position vector is changing. The rate of change of displacement of a body is defined as velocity. It is a physical quantity that is affected by both the motion’s direction and the speed’s magnitude. The magnitude of the rate of change of location is given by the scalar quantity speed. The direction is involved in the velocity, which is a specific instance of speed. The motion should have a consistent speed and direction in order for the velocity to be uniform.