Answer the following question given this paragraph: 

Figure 9.3 This car is in dynamic equilibrium because it is moving at constant velocity. There are horizontal and vertical forces, but the net external force in any direction is zero. The applied force F app between the tires and the road is balanced by air friction, and the weight of the car is supported by the normal forces, here shown to be equal for all four tires.


Q: When is a moving car said to be in dynamic equilibrium?

 Choices:

- at rest

- at homeostasis

- when accelerating

- zero net force

A:
zero net force
