Question

what does it mean for an object's velocity and acceleration to be in opposite directions?

Answer 1

Velocity and acceleration are vectors, which contain a direction and a magnitude. For example, if you're in a car and stopping at a red light, you're decelerating. As your velocity decreases the vector of your deceleration is pointing in the opposite direction of your velocity as you slow down. You are still moving forward but you're "accelerating" in the opposite direction. Give me a medal