Seeking the commonly used electrical formulas in high school physics

Seeking the commonly used electrical formulas in high school physics

Ohm's law I = u / R and the deformation formula of Ohm's law r = u / I, u = IR, e = U1 + U2 + (this is the sum of the voltages of the branches in the series circuit, equal to the electromotive force of the power supply, and the total current is the same). In terms of electric field, f electric field = EQ, I = the change of magnetic flux / T

The result of "10 meter turn back run" reflects the sensitive quality of human body. In the test, on the straight track, the subjects stand in front of the starting and finishing line in a standing starting position. After hearing the command of "run", they run to the turn back line 10 meters ahead with all their strength. The tester starts to count the time at the same time. When the subjects arrive at the turn back line, they touch the object (such as wooden box) at the turn back line with their hands, and then run again Turn around and run to the starting and finishing line. When the chest reaches the vertical plane of the starting and finishing line, the tester stops the watch, and the time taken is the result of "10 meter turn back run". Suppose that the acceleration of the subject at the start is 4 mgs2, and the maximum speed in the process of movement is 4 m / s. when he reaches the turn back line, he needs to decelerate to zero, and the acceleration of deceleration is 8 m / S2. When he returns, he does not need to decelerate after reaching the maximum speed (1) the time for the subject to move at a constant speed in the process of the first 10 meters; (2) the number of seconds for the subject's "10 meter turn back run"?

(1) For the subjects, in the process of moving from the starting point to the end line to the turn back line: acceleration stage: T1 = VMA1 = 44s = 1s, acceleration displacement: X1 = 12vmt1 = 2m, deceleration stage: T2 = vma2 = 48S = 0.5s, deceleration displacement: x2 = 12vmt2 = 12 × 4 × 0.5m = 1m, so: the displacement in the uniform speed stage: X3 = 10-2-1m = 7m, the time of uniform deceleration movement: T = x3vm (2) in the process of moving from the turn back line to the starting and finishing line: acceleration phase: movement time T3 = VMA1 = 1s, acceleration phase displacement: X4 = 12vmt3 = 2m, time T4 = l − x4vm = 10 − 24s = 2S, so the total score of the subject is: t = T1 + T2 + T uniform + T3 + T4 = 6.25s The result of "10 meter turn back run" was 6.25s

A force F is decomposed into F1 and F2. If the resultant force F = 40n, the angle between F1 and F is 30 ° as shown in the figure. If F2 takes a certain value, F1 can have two different values, then the value range of F2 is______ ．

Because the vertical segment is the shortest, we know that when the component force F2 is perpendicular to the component force F1, F2 is the smallest. As shown in the figure, then F2 = fsin30 ° = 40 × 12n = 20n. So as long as it is greater than 20n, it is possible to be less than 40n; therefore, the answer is: 20n < F2 < 40n