Final answer:
Both statements the student asked about are true: Velocity can be positive or negative depending on direction, and the time interval Δt is always positive.
Step-by-step explanation:
The correct answer to the student's question is that both statements are true: Velocity can be positive or negative, depending on the direction of the displacement, and the time interval, Δt, is always positive.
Velocity is a vector quantity, meaning it has both magnitude and direction. It can be positive if the object is moving in the direction chosen as positive in the coordinate system, or negative if it's moving in the opposite direction. The time interval is a scalar quantity which represents the difference in time between two events; since it is a measure of duration, it cannot be negative.
Explanation of Velocity
Velocity indicates the rate at which an object changes its position. If an object moves from one point to another, the direction of its displacement is factored into its velocity, with the sign (positive or negative) indicating this direction relative to a chosen coordinate system.
Explanation of Time Interval
The time interval (Δt) is simply the difference in time from one point to another. Because it represents a duration, it is inherently positive, as one cannot travel back in time or have a negative amount of time pass between events.