When a vehicle travels at a steady speed the driving force and the resistive forces must be __________. What one word completes sentence?

The one word that completes the sentence is "equal."

When a vehicle travels at a steady speed, it means that it is not accelerating or decelerating. According to Newton's first law of motion, an object in motion will stay in motion at a constant speed unless acted upon by an external force. In this case, the driving force exerted by the engine of the vehicle must be equal to the resistive forces opposing the motion, such as friction, air resistance, and rolling resistance. When these forces are equal, the net force acting on the vehicle is zero, allowing it to maintain a constant speed. Therefore, in such a situation, the balance between these forces is crucial for steady motion.