Which of the following quantities is directly proportional to the time interval after a projectile has left th

Question

Which of the following quantities is directly proportional to the time interval after a projectile has left the barrel that shot it out? The x-axis is horizontal; the y-axis is vertically upward.

∆|v|

Day

Dy

∆|r|

Dvy

Answer 1

The horizontal distance between the end of the barrel and the projectile's position.

However, I do not understand the notation used sufficiently to give you one of those answers. Variables in a physics question ought to be defined.