Final answer:
The force of the truck pulling the car and the car pulling against the truck are equal due to Newton's third law. When the car brakes, it causes unbalanced forces, leading the truck to slow down.
Step-by-step explanation:
Answer to the Student's Question
The force of the truck pulling the car is equal to that of the car pulling against the truck. This is due to Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. So, when the truck exerts a force to tow the car, the car exerts an equal force in the opposite direction.
If the car's brakes are applied while being towed, the forces become unbalanced, causing the truck to slow down. This scenario involves both friction and tension forces and, depending on the force the car's brakes exert, may result in a decrease of the tension in the pulling cable.