The supreme question of physics is difficult to solve all living beings, and a question of high scho

This question is about the conservation of momentum and energy. It's not very difficult.

The elastic potential energy of the spring is determined by the deformation of the spring, if the speed of the wooden block is greater than the speed of the wooden plank, it will continue to compress the spring, only when the velocity of the wooden block is equal to the speed of the wooden plank, the spring can no longer be compressed, so only at this time the spring has the maximum elastic potential energy.

Solution: When the velocity of the block and the board is equal, the spring has the maximum elastic potential energy, and let their velocities be v at this time

1, the first common velocity i.e. before the collision to the right Energy conservation 1 2mv0 2=1 2mv1 2+1 2mv1 2+wf1+ep

Conservation of momentum mv0=mv1+mv1

2. The second co-velocity is to the left after the collision of the wooden block At this time, the wooden block continues to the right The elastic potential energy is the largest, that is, the displacement of the wooden block relative to the template is the largest, that is, when the wooden block is at rest relative to the wooden board (at this time, the speed you said is 0, but it is relative to the wooden plank), that is, the second co-velocity of the wooden board and the wooden block (the first co-velocity to the right) Energy conservation 1 2mv1 2+1 2mv1 2+ep=1 2mv2 2+1 2mv2 2+ep is the maximum.

Conservation of momentum mv1-mv1=mv2+mv2

3, the third common velocity, that is, when the spring pushes the wooden block to the leftmost end of the plank and stops, the momentum is conserved v3=v2

Conservation of energy The kinetic energy of the wooden block and the wooden board does not change, the elastic potential energy is converted into heat consumption through the work done by frictional force, i.e., ep max = wf2 and the work done by friction is the same as the work done from left to right at the beginning (because the wood block returns to its original position, that is, the displacement of the relative plank is the same as the first time), so wf2 = wf1 = ep is maximum.

Solution: ep max = 15 64 v0 2

A is correct. If there is an anticlockwise current in a and it is enhanced, the magnetic flux perpendicular to the paper side of the B coil increases, and it can be seen from Lenz's law that the current in the "inverse" B coil will produce a magnetic field perpendicular to the paper face, and the current is in the clockwise direction from the ampere rule. From the attraction of the same direction of the electric furnace flow and the repulsion of the reverse current, the expansion of coil B can be seen.

The idea of choosing b and b is correct, the idea of (1) is correct, and the current in (2) is not right in "the current in coil b is in a clockwise direction, which is opposite to the current direction of a, and has a repulsive effect", and it should be attracted to each other.

Choose A, right-handed rule first, then left-handed rule.

Belch. Really big deal. Dizzy. It's hard to be the subject.

This question of yours is actually not a difficult physics, I don't know if the question you got from ** is your own imagination. First of all, whether a fracture is broken, in addition to the height, is related to the air resistance of the fall, in this question it can be considered that the size is directly proportional to the falling speed (the scale coefficient is not related to the surface area of the clothing, but to the area of the person in the horizontal plane, and the shape of the human body, for example, the Harmony is streamlined, the coefficient is small, and it is generally measured by the test method). Thus, according to the second law of the ox, the kinetic equation can be listed, and the velocity of the person before landing can be solved, and then the higher one will calculate the force on the person according to the momentum (the magnitude of the force is the time when the speed of the person and the ground is zero, which is related to the personal experience and the situation of the ground, such as cement or cotton when the ground is on the ground, the result is not the same).

Based on the calculated force and the ability of the person's bones to withstand (which is relevant to the individual), it is possible to determine whether a fracture is broken.

I hope you can understand the above analysis. Calculate it yourself according to your needs. However, the surface area of the garment cannot be calculated.

ps: The owner of the house is like a novice Note: t 2 is the square of t, and the other 2 also represents the quadratic.

5 2 is five out of two, and the other is also the score line.

Question 1: Method: According to the formula δs=nat 2 (n=10-3=7, t=1).

This yields a=1m s2

Method : According to the formula s=vt+1 2at 2

It is obtained that s(third) = s (first three) - s (first two) = v+5 2a

s (tenth) = s (former division) - s (first nine) = v + 19 2a

s(tenth)-s(third) = 14 2a

And because s(tenth)-s(third)=7

So a=1m s 2

Question 2: According to the formula s=vt+1 2at 2 combined with s=4t-t 2 in the question

This gives v=4 and 1 2a=-1

That is, the initial velocity is 4 and the acceleration is -2

Q1 The average velocity in the fourth second is (v4+v3) 2, which is the instantaneous velocity in the second.

According to the formula v=v (initial velocity) + at

v（s=vt=-3*1=-3

The second question is according to the formula v 2-v (initial velocity) 2=2as

v=5. s=-9/4

Hehe, I hit a lot, but, it's not hard, hehe.

The minimum resultant force is when the direction of the two forces is opposite.

Maximum is when the direction of two forces is the same.

The subtraction of two forces is equal to a

The addition is equal to the b solution: let the two forces be f1 f2 and f2 f1 respectively

From the title: f2 f1 a

f2＋f1＝b

So: f2 (a b) 2

f1＝(b－a)/2

Later you do it yourself.

These two forces are set to f1 and f2, f1 f2, because the resultant force is the largest when the two forces are in the same direction, and the net force is the smallest when the direction is opposite, so f1-f2 a, f1+f2 b, f1 (a+b) 2, f2 (b-a) 2, then when these two forces are perpendicular, the magnitude is calculated by the Pythagorean theorem, and the result should be (a square + b squared) 2

Please read it carefully, if you don't understand, you can hi me.

1. Because the internal resistance is not counted, and the voltmeter can be regarded as a G meter (galvanometer) in series with a large resistance, so V (that is, the outermost layer) must be the voltage of all resistances, in fact, it is the power supply voltage, so the power supply voltage E=24V

2. In the same way, V1 measures the voltage of R1 with a large resistance in parallel. 1 r total 1 = 1 r 1 + 1 2k

So r total 1=r1 2k (r1+2k).

And because the power supply voltage is 24V, the local circuit voltage is 6V, so R2 must be the same as the current of the 18V series circuit, so 6 R total 1=18 R23, the same, V2 measures the voltage of R2 parallel large resistance. 1 r total 2 = 1 r2 + 1 2k

So r total 2=r2 2k (r2+2k).

And because the power supply voltage is 24V, the local circuit voltage is 12V, so R1 must be the same as the current of the 12V series circuit, so 12 R total 2 = 12 R14, Bili 6 R total 1 = 18 R2 and 12 R total 2 = 12 R1, that is, 24000R2 + 12R1r2 = 72000R124000R1 + 12R1r2 = 24000R2 solution r1 = 1000 ohms, r2 = 2000 ohms If the answer is wrong, you can find me.

The electromotive force of the power supply is , the internal resistance is not counted, and the total voltage of R1 and R2 is measured to be 24V, so:

E=24V The voltage measured across R2 is 12V:

i2=12/[rvr2/(rv+r2)]=12(rv+r2)/(rvr2)=12(2000+r2)/(2000r2)

e=i2r1+12, that is, 24=i2r1+12, i2=(24-12) r1=12 r1, substituting the above equation to obtain:

12/r1=12(2000+r2)/(2000r2)

r1(2000+r2)=2000r2

2000r1+r1r2=2000r2...1)

The voltage at both ends of R1 is measured to be 6V:

i1=6/(rvr1/(rv+r1)]=6(rv+r1)/(rvr1)=6(2000+r1)/(2000r1)

e=i1r2+6, that is: 24=i1r2+6, i1=(24-6) r2=18 r2 is substituted into the above equation to obtain:

18/r2=6(2000+r1)/(2000r1)

r2(2000+r1)=6000r1

2000r2+r1r2=6000r1...2)

Solve simultaneous equations (1) and (2) to obtain:

r1=1000ω

r2=2000ω

The intensity in the accelerating electric field is e=u d

d does not change, so the electric field strength is determined by u.

The number of particles that are accelerating in the electric field is n

The electric field force experienced by each particle is f=2ee=2eu d, and the electric field force experienced by all particles is f=2neu d

According to Newton's third law, the reaction force of the spacecraft is f=2neu d, and the force f should be changed to ·2f to choose ac

Pick B. From the momentum theorem, ft=nmv, from the kinetic energy theorem, 2eu=(mv 2) 2, and because the electron does a uniform linear motion with an initial velocity of 0, it is solved by t=d (v 2) to obtain f=2neu dIn order to change the recoil force obtained by the accelerator to 2f, option ac is correct.