An underwater survey vehicle moves along a straight north–south route. North is chosen as the positive direction.
For one interval of its journey, the vehicle's velocity–time graph is a horizontal line below the time axis at -3.5 m/s.
Which statement describes the motion of the vehicle during this interval?
It travels south at a constant velocity with zero acceleration.
It travels south and its speed increases at a steady rate.
It travels north and its speed decreases at a steady rate.
It travels north at a constant velocity with zero acceleration.