Chapter 28 Chapter Twenty Seven

Not long after Jiang Wei left, Forensic Chen brought the teacher from the Mechanics Laboratory of Zhejiang University to Gao Dong. "Boss, this is Teacher Qi." Gao Dong stretched out his hand to ask for a seat, poured a glass of water and put it in front of the other party, and said, "Mr. Qi, Lao Chen has already told you about the relevant situation. This case is relatively important and sensitive, so I don't want to be too polite. Let me tell you about it." the experimental results." Professor Qi said slowly: "We have done several experiments, and finally judged that the stone slab fell from the fifth, sixth or seventh floors. Since the direction and position of the stone slab when it fell cannot be determined, the situation of hitting the ground after falling is also uncertain. It is impossible to calculate exactly, so all three floors are possible—”

Gao Dong interrupted him: "The median value is the sixth floor, right?" "Well... yes, but the probability of these three floors is the same—" "We have investigated this point and found out that it is the sixth floor, because some witnesses saw that someone erected this stone slab to the edge of the edge of the cement rainshield outside the window on the sixth floor." Professor Qi shut his mouth in embarrassment. Their work was only through experiments to determine from which floor the stone slab fell. Since Gao Dong already had the answer, their results were of little use.

Gao Dong continued: "But now I have a question, Mr. Qi, in your opinion, if someone throws a stone slab down on the sixth floor, what is the probability of hitting Hu Haiping?" "It's very low, because the height of the sixth floor is about 20 meters, and it takes two seconds for an object to fall 20 meters freely. We experimented with that stone slab. Since the center of gravity of the stone slab is not completely uniform, when the stone slab falls, it will not fall. It is in a horizontal state, but slightly inclined, and the width of the horizontal projection is about 40 to 50 centimeters. If it is really like the situation you mentioned in Bureau Gao, the people upstairs need to estimate that the victim is within two feet before throwing the stone slab. Seconds later, it was just in a narrow area within 50 centimeters. The walking speed of a normal person is about two meters per second. That is to say, the time judgment accuracy error of the person throwing the stone slab cannot exceed a quarter of a second."

Gao Dong thought about Professor Qi's words, and drew the scene of Hu Haiping's murder in his mind. When Hu Haiping was about four meters away from the rainshield on the first floor, the stone slab on the sixth floor began to fall. Two seconds later, Hu Haiping stepped into the fatal area with a width of "fifty centimeters" and was hit by the stone slab to death. Professor Qi continued: "This is the simplest case. The calculation is the time required for the slab to do free fall. The premise is that the people on the sixth floor threw the slate into the air at a relatively horizontal position and dropped it down. But the slate is very heavy, and I think few people can throw the slate. It is more likely that the person pushed the slate down."

"Oh? What's the difference between pushing it down and throwing it out?" "The time required to push it down is even more complicated." Professor Qi took a sip and continued, "If the stone slab was standing on the edge at that time, and someone pushed it down, then the movement would have to be broken down into two parts. Stage. In the first stage, the bottom side of the slab is still supported by the edge of the flashing, and the top of the slab is tilted outward in the air. When it is tilted to a horizontal position, the supported side is also separated from the flashing. Then comes the second stage , the slate starts to do free fall motion. In the first stage, the slab makes a circular arc flipping motion. The time of this flip is difficult to calculate accurately, because if the pushing force is large, the flipping process will be short. On the contrary, The less you push, the longer it takes to flip."

"How long do you estimate this flipping process will take?" "About a few tenths of a second, it should be more than a quarter of a second." Gao Dong frowned, this time the problem was more complicated than his original assumption. Originally, he thought that if the murderer wanted to smash Hu Haiping to death, he must have calculated the speed and time, and these tasks were not as complicated as imagined. The murderer only needs to use a stopwatch to accurately calculate the speed at which Hu Haiping walks towards the unit building through repeated and continuous tracking, and then calculate the time it takes for the stone slab to fall from the sixth floor to the top of Hu Haiping's head, and then make a mark on the ground. As soon as he reached the mark, he began to throw down the stone slab. As long as Hu Haiping walked at the same speed as usual, the success rate of the final murder was very high.

But now Professor Qi's words gave him new thinking. The slate is very heavy, and it is very difficult for an adult man to lift it up, but after you lift it up, you have to maintain a horizontal state and throw it forward.The throwing force was weak, and the stone slab directly hit the rainshield on the sixth floor.But when the throwing force is strong enough, the stone slab will be displaced in the horizontal direction, which is equivalent to a parabolic motion, and it is difficult to hit Hu Haiping when it hits the ground. From a common sense point of view, it is rare for an adult man to lift a stone slab and throw it with this level of strength, and it is even more impossible to throw it at an appropriate timing.

It seems that the stone slab should have been standing on the edge and pushed down. But the problem with this link is that the moment the stone slab is pushed down, the stone slab does not fall freely directly, but first performs an overturning movement. Start doing free fall. And the flipping motion takes a few tenths of a second. But the prerequisite for the murderer to succeed in the crime is to calculate all the time required for the stone slab to fall, and accurately control the error within a quarter of a second. Gao Dong pursed his lips, he now has two judgments: The first is that the murderer's murder this time also had a large part of luck. Perhaps he never thought that the falling process of the stone slab was so complicated. It was entirely based on the situation and roughly estimated Hu Haiping's position.Or he would calculate the time of free fall, calculate the whole process as free fall, and the result was successful.

This is due to his good luck. The second situation is that the murderer did not rely on luck to complete the murder. He even accurately calculated the time required for the two stages of the stone slab falling.Calculus was used in the calculation of time in the first stage, and Gao Dong had long thrown away the knowledge of calculus he had learned in college. If the murderer can use calculus, what is the identity of the murderer? Gao Dong glanced at Professor Qi. That's right, if the murderer doesn't rely on luck to kill, then the murderer's occupation cannot escape teachers, engineers or people who have just graduated from college for a few years.

What about Ye Yuanchao? It seems impossible, he will never know calculus at his age.Thirty years ago he would not know calculus.He is sure he will never know calculus in his life. But the question is, did the murderer rely on luck to commit the crime this time, or did he rely on the inevitable chance of winning?