You can imagine that the solid ball landed first. A large solid paper ball (note that it is a paper ball, and any part of the ball is real paper, not our group's paper ball, hehe) or a hollow paper ball with the same volume, which will land first? Obviously, the solid paper ball will land first, right? Because the air resistance is too different from the gravity of the solid ball, the effect is too small to play a major role at all, but it plays a big role in the hollow ball, because its gravity is similar to the air resistance, so the iron ball is the same. On the other hand, when we think about it again, it is actually wrong. If we have no air resistance, two balls will land at the same time. According to the formula used by the landlord, one ball has a large acceleration and the other ball has a small acceleration. How is that possible? In fact, this question itself is not rigorous, because it is not clear what the hollow part of the hollow ball is and how empty it is. If it is a thin hollow ball with a vacuum inside, the buoyancy may be greater than gravity, but the questioner should ignore this situation, and the conclusion is consistent with the answer to the question, so we will not discuss it. As for the algorithm of two balls landing, I won't explain it because of the time. I just remind you that your algorithm ignores the magnitude of acceleration. Look at the formula yourself. What is the acceleration equal to? Another point is that the landlord thinks that the air resistance of the two balls is the same.