The argument that best supports the student's claim is: Heavier objects need greater force than lighter objects to accelerate at the same rate.
This is derived from Newton's second law of motion, which states that \( F = ma \) (force equals mass times acceleration). Since both boxes are subjected to the same force (40 N), but box 1 accelerates more (10 m/s²) compared to box 2 (5 m/s²), it must have a smaller mass. Therefore, the reasoning that heavier objects require greater force to achieve the same acceleration supports the student's claim that box 1 (less mass) accelerates more than box 2 (greater mass) under the same force.