Net force changes after link breaks Steps:

• Initially, engine and truck move at constant speed, so net force on system is zero; driving force balances total friction.
• Link breaks, removing tension force between them.
• Truck now has unbalanced friction backward, causing deceleration.
• Engine's driving force exceeds its own friction, causing acceleration.

Why A is correct:

• Newton's second law (F=ma): unbalanced forces cause truck to decelerate gradually and engine to accelerate.

Why the others are wrong:

• B: Engine accelerates due to net forward force; truck decelerates gradually, not stops immediately.
• C: Engine accelerates, speed does not stay constant.
• D: Truck decelerates gradually, does not stop immediately.

Final answer: A