Answer:
Riding a car down the street: Velocity is constant and acceleration is zero.
Coming to a red light: Velocity decreases and acceleration is negative.
Waiting for the green light: Velocity is zero and acceleration is zero.
Starting off again: Velocity increases and acceleration is positive.
Explanation:
Velocity is a change in position, and acceleration a change in velocity.
When we have a positive acceleration, velocity will increase, and when we have negative acceleration, velocity will decrease.
Likewise, since we can only observe changes in position, an increase in velocity will tell us that the acceleration is positive, and a decrease in velocity will tell us that the acceleration is negative.
When acceleration is zero, the object in motion is said to be at rest, that is, at constant velocity. It can be zero (at the red light), or any other constant number (riding down the street).
