The correct selection is speed.

Speed refers to how fast an object is moving, while velocity includes both speed and direction. Hence, when the car is described as traveling 75 miles per hour north, it's velocity because it includes both the speed (75 miles per hour) and the direction (north).

Would you like further details or have any questions?

Here are 5 related questions to deepen your understanding:

1. What is the difference between scalar and vector quantities?
2. How do you calculate average velocity?
3. Can speed ever be negative? Why or why not?
4. How does acceleration relate to velocity?
5. What happens to velocity when the direction of travel changes?

Tip: Speed is a scalar quantity (magnitude only), while velocity is a vector (magnitude and direction).