Question

a v-t line below the axis indicates: negative velocity; position is constant; positive acceleration; speed is zero

Explanation:

In a velocity - time (v - t) graph, the sign of the velocity is determined by its position relative to the time axis (t - axis). Velocity is a vector quantity, which means it has both magnitude and direction. When the v - t line is below the time axis, it indicates that the velocity has a negative value. This negative value represents a direction opposite to the positive direction (usually defined as the forward or positive - direction of motion).

• For the option "position is constant": A constant position would be represented by a velocity of zero (a horizontal line on the v - t graph along the t - axis), not a line below the axis.
• For the option "positive acceleration": Acceleration is the slope of the v - t graph. A positive acceleration would be indicated by a positive slope, and it has nothing to do with the position of the line above or below the axis.
• For the option "speed is zero": Speed is the magnitude of velocity. A speed of zero would be represented by the velocity - time line coinciding with the t - axis (v = 0), not below it.

Answer:

A. negative velocity