Talk about several big physics problems

21. Emergency braking is regarded as a linear motion with uniform acceleration, and the time and distance are all given. Let's work out a set of formulas to calculate the speed before braking of 12m/s, and then convert it. It is speeding.

22. This picture will be easier to understand, and the total height should be 16/15 of AB, that is, (v? )/(v? -(v/4)? ), then it's easy to analyze

(1). This is also a set of formulas, which is relatively basic, not to mention, 8m/s

(2). This time is the time from point B to the apex, and then falls to point A, and the whole process is symmetrical. If the upward speed is positive, then the speed of point B is 2m/s (1/4 of v), and when it falls back to point A. . .

to get to the point, this paper uses the conditions of opening the parachute first and then slowing down evenly to find the speed when opening the parachute, and then uses the free fall to find other values

(1). The number is disgusting, and I don't want to forget it. . .

(2). Same as above. . .