When a car’s velocity is negative and its acceleration is positive, what is happening to the car’s motion?

Question

a.
The car speeds up.
b.
The car slows down.
c.
The car remains at rest.
d.
The car travels at constant speed

Answer 1

The reasoning in the other answer is completely wrong.

If velocity is negative (let's say, "left") and acceleration is positive (therefore "right"), then the velocity (NOT the speed) is increasing. "Increasing" in this context means "becoming less negative" -- heading toward zero. Therefore → b. The car slows down.



Simple thought experiment. Take a coordinate system where "up" is negative. Toss an object "up". It has negative velocity. Gravity is working in the other direction, so the acceleration is positive. The object will slow down until its velocity is zero; then it will attain positive velocity. All during this time the velocity is increasing. (The speed is decreasing and then increasing.)



I hope that helps.

Answer 2

Since velocity is a vector and it is negative, you can assume that the car is traveling in whatever the opposite direction traveling "forward" would be; that is, it's traveling backwards in regards to the reference point (probably that's itself). If its acceleration is positive, that means its SPEED is increasing; so if its speed is increasing and it's traveling backwards, the best option of these is a.