Final answer:
A car traveling 45 mph westward is described as having a velocity, which is both a speed with magnitude and a specified direction.
Step-by-step explanation:
When a car is traveling 45 mph westward, it is described as having a velocity. Velocity is a vector quantity which means it includes both magnitude and direction. In this example, 45 mph provides the magnitude of the speed, and 'westward' provides the direction of the motion, collectively defining the velocity of the car.
If you divide the total distance traveled on a car trip (as determined by the odometer) by the time for the trip, you are calculating the average speed, which is a scalar quantity and does not take direction into account. To determine the magnitude of the average velocity, you would need to consider the overall displacement from start to finish and the time for the trip.