1 elevator problem

Whether people can jump in the elevator, we must first understand the meaning of "jump", that is to say, as long as the glue leaves the elevator and changes to the ground of inertial reference system, even if people jump, they must first touch the ground (in the reference system). If the Chinese meaning of jump is not considered, the acceleration of free fall of any elevator = acceleration of gravity. There is no relative acceleration and interaction between any elevators, so people can move freely in the elevators, just like astronauts, and they can't be considered as particles, so my point is that if you leave the ground (in the inertial system), even if you jump, it is completely possible. As long as you simply extend your legs downward (whether you touch an object or not), there will be relative displacement. Because the legs have inertia, all objects are equivalent in the elevator frame of reference and are not affected by gravity. When you stretch your legs downward, you will have a reaction to the human body, so you can produce force, relative speed, downward blowing and so on.

2 the problem of birds

First of all, I think this problem should include air resistance. The speed of a bird's free fall is 10 second. As the speed increases, the air resistance also increases. Finally, the air resistance will be equal to gravity, because the density of air is increasing, the resistance will be greater than gravity. I know that if I make a speed image, the final appearance of the image should be a line (acceleration) with a small slope.

Whether a bird can fly depends on the height h at the beginning of its free fall. Assuming that the ideal state (without air resistance) is that the bird's mass is m and the maximum lift generated by the bird's wings is f, the following formula can be derived (G= 10): the displacement of the bird before 10 second = 1/2GT 2 = the acceleration of the bird after being stressed = (f-).

There is a question: why not G-F? You followed the evidence and proved that the former is not the latter.

There is no doubt that a bird with normal evidence can take off when it takes off. The acceleration at takeoff is upward, so it is the former. (The time taken by the bird to exert its strength is not considered here. ) The time when the bird decelerates to the falling speed of 0 =100/(f-g)/m = t.

The average speed during deceleration =50 (when explaining the instantaneous speed at the middle time, draw the speed-time image, and you can get two congruent triangles at the middle time. Why is the small triangle above replaced by the congruent triangle below? Displacement = area =T*V0/2).

When the fall decelerates to zero displacement.

50* 100/(F-G)/M+500[ actually, this value is very small due to the help of air resistance] < > H

Comparing the size, because there are many variables, this problem can not be solved only by hypothetical model, but by actual measurement and verification.

three

Without considering the gravitational resistance, you forget the basic principle to be concerned about as a long-distance thermal shot. The geostrophic deflection is to the left in the northern hemisphere and to the right in the southern hemisphere. Even if the bullet's advance is not considered, it is completely correct to draw the map that will hit at that time. This problem is abstracted into a mathematical model, that is, the intersection problem in the three-dimensional coordinate system 1, the intersection point 2, each flight displacement is long/each time is equal, so it is possible to hit.

In practice, there are too many variables, and the position and moving direction of the plane relative to the shooter are very important. If the plane dived at a 90-degree angle with this person, it would be too easy to hit it. If you are flying sideways, at least a detector that detects various variables at all times, a computer that is almost the same, and the accuracy error of the gun is very small. At this time, it is very unlikely to win a goal far away from 100 with paper balls in the storm. I'm done with my opinion.