Final answer:
When a car is going around a curve at a constant speed, it is accelerating due to the change in direction, not because the speed itself is changing. The velocity, which includes direction, is not constant even if the speed is.
Step-by-step explanation:
If you are in a car that is going around a curve and the speedometer reads a constant 30 miles per hour, the following is not true: C. Your velocity is constant. While your speed is constant since the speedometer shows a constant 30 mph, your velocity is not constant because velocity is a vector quantity that includes both magnitude and direction. As you go around a curve, your direction is changing, which means your velocity is changing. This is considered acceleration, even when the magnitude (the speed) remains constant.
Therefore, the correct statement about a car moving at a constant speed in a single direction on a straight road is d. The car is accelerating because neither the magnitude nor the direction of velocity is changing. In this case, since neither speed nor direction is changing, there is no acceleration. This is different from the scenario where the car is turning and thus changing direction. Again, an object (such as the car in our example) can accelerate by speeding up, slowing down, or changing direction.