The force of gravity acting on the car increases. The force of gravity acting on the car decreases. The forces influencing the car are not balanced. The forces influencing the car are balanced.
I gave my students this multiple choice question: A toy car rolls at a constant speed down a straight inclined track. When the car reaches the flat surface at the base of the inclined track, the speed of the car decreases. Which statement best explains why the speed of the car decreases when it reaches the flat surface?

Only one answer is correct among these 4 choices:
- The force of gravity acting on the car increases.
- The force of gravity acting on the car decreases.
- The forces influencing the car are not balanced.
- The forces influencing the car are balanced.

Could you tell me which one is correct?

The forces influencing the car are not balanced.