Very difficult physics problems, master advance!

One by one.

1. For example, if the person carries the bucket for example, if it is lifted and completely immovable, the ideal situation is that the bucket will not consume the energy of the human body after it is lifted, but the reality is not the case, the muscle fibers of the human body provide force to overcome the gravity of the bucket in the case of tension, if the force provided by the muscle fiber tension always maintains this fixed value, it is equivalent to a stone statue at this time, and it will not consume energy. But the fact is that we feel sore after maintaining it for a period of time, this soreness ** produces lactic acid in anaerobic respiration of muscles, why is there lactic acid produced, this is because human muscles cannot provide constant force of the bucket like a stone statue, this force is a variable force, large and small, that is to say, the height of the bucket is constantly changing in the actual situation, and the muscles will be tense and relaxed in this process, and the muscles will consume energy in this process.

2. There are two situations for the motor to lift the elevator:

Clause. First, the elevator is not overweight. In this case, the motor does not convert energy to the elevator, the reason why the elevator does not move, is because the motor does not rotate, the elevator does not rotate because the motor is generally equipped with electromagnetic brakes, this device can lock the motor shaft after power-on, and the motor shaft can rotate freely after power-off, then it can be known that the energy consumption of the motor at this time is on the electromagnetic brake, it locks the motor shaft, and the elevator will not move;

Clause. Second, the elevator is overweight. In this case, the pulling force provided by the motor is less than the gravity of the elevator, the axial force of the motor is too small to rotate, the electromagnetic brake has no effect at this time, the current passes through the winding of the motor, and the energy obtained by the motor is all converted into the heat energy of the internal circuit, and the heat generation is much greater than when it rotates, and the energy of the motor will not be transferred to the elevator but converted into a large amount of heat, which is why the motor is easy to burn out when it is overloaded.

Haha, I'll give you another question Mention that the bucket consumes human energy (chemical energy can also be said to be biological energy) to convert into the potential energy of the bucket, so doesn't the process of putting down the bucket consume human energy Turn to ** Even the potential energy of the bucket is less Hehe.

Teach you the analytical methods for analyzing energy conversion problems, 1 from the result analysis process 2 analysis process to find the result. The problem you said and the question I gave you are easy to understand by analyzing it in the first way. That is, first analyze what forms of energy may be involved in the transformation, and then analyze how it is transformed.

The process of lifting the bucket energy may be converted between gravitational potential energy, the chemical energy of the human body and the thermal energy, and the problem is solved in half. In the analysis process... In the process of lowering the bucket, the chemical energy of the human body, the gravitational potential energy of the bucket, and the potential energy of the bucket are converted into heat energy through the stretching and twisting of the muscles.

The electric motor stops in the air with the gondola, and the electrical energy consumed by the electric motor is converted into heat. For there is no other form of energy involved in the transformation ... It's as simple as that, and then you're in the process of analyzing the results by this.

If you don't supply power to the elevator, will the elevator fall? When the cable is not powered by the motor, it is fixed and has a pulling force; It doesn't fall even if the power goes out. Otherwise, as soon as the power goes out, the elevator will fall, and the elevator damage rate is extremely high, because power outages are commonplace. So the motor has no power consumption.

And when a person lifts a bucket, the force exerted by the human arm does not do work. But to generate this force, multiple organs in the body need to consume energy. So the energy is not spent on the bucket, but on the pulling force.

It is the power consumption of the work of the internal organs of the human body, and the energy consumed by chemical reactions such as heat dissipation, muscle contraction, and lactic acid production.

The object has gravity, the elevator is pulled upwards by the wire rope, the provider of the pulling force comes from the electrical energy, if the current disappears, the steel wire will no longer provide the pulling force, the elevator falls, so the current remains constant to provide electrical energy to fight against the gravitational potential energy generated by gravity.

Consumed bioenergy is converted into sweat or other metabolites.

Haha, I've thought about this too, and the power will be cut off right away, and I'll give it to you tomorrow.

。。The landlord's question is interesting, I'll copy it first, think about it later.

The spring is connected with the temperature-sensitive magnet, at the bottom of the inner tank, when the key is not pressed, although the magnet is magnetic at this time, but because there is a distance between the temperature-sensitive magnet and the permanent magnet, they are not attracted to each other, (you can try it, turn on the switch, put in the inner tank, if you don't press the button at this time, the key will not be in the lowest position), the inner tank is pressed against the spring, so the spring is compressed.

If it is not put into the inner tank, the spring is not pressed, then it is not the original length state at this time When the two magnets attract each other, the temperature sensing magnet drives one end of the spring connected to it, and the other end of the spring is fixed in a position, at this time, the temperature sensing magnet is attracted downward, and the spring is elongated.

I also pressed the rice cooker just now, you can try it, feel it, welcome to ask.

When it is not working, it is in a low temperature state, and the temperature-sensing magnet is magnetic, and the spring is compressed.

First of all, the spring cannot be in an elongated state, when the rice cooker does not put the inner tank into the spring is not affected by gravity in the original state, after putting the inner tank into the spring due to the action of gravity, the spring is in a compressed state, when the key is pressed, the permanent magnet and the temperature sensing magnet are engaged, which has nothing to do with the spring, so it has been in a compression state. You can think about it. It's okay to take a rice cooker and study it.

1.The average speed of a small high run of 100m is.

v=s/t=100m/

2.Xiao Gao has the fastest speed in the 5th 20m, and the average speed is the shortest time and the maximum speed in the second 20s, v=s t=20m, t2=, t3=, t4=, t5=

T1, T2, T4 are less than, and therefore less than, the average velocity.

To improve his performance, he can increase his starting speed.

Meaning of the title: Start from a standstill, accelerate the movement with A1 = uniform, drive at a constant speed later, and then move with the size A2 = uniform deceleration until it stops, a total of 130 seconds, and a travel of 1600 meters.

Solution: (1) Let the time of the uniform acceleration phase be t1 and the displacement is s1; The time of the phase of uniform motion is t2 and the displacement is s2; The time of the uniform deceleration motion phase is t3 and the displacement is s3.

Then t, total t1, t2, t3 130 seconds.

Total S1 S2 S3 1600 m.

In the uniform acceleration phase, there is S1 (VM2) *T1 .Equation 1

vm＝a1*t1 ..Equation 2

In the phase of constant motion, there is S2 vm*t2 .Equation 3

In the phase of uniform deceleration motion, there is S3 (VM2) *T3 .Equation 4

vm＝a2*t3 ..Equation 5

From the equation we get s total vm*(t total t2) 2

i.e. 1600 VM*(130 T2)2 ...Equation 6

From the equation (t, total t2) (vm a1) (vm a2).

i.e. 130 t2 (vm Eq. 7

From equations 6 and 7 are synthetically obtained t2 120 seconds, and the maximum velocity vm m s is obtained

2) If the motorcycle starts from a standstill, A1 and A2 remain unchanged until it stops, and the stroke remains unchanged, and the total Vm * (Total T2) 2 has been obtained from the previous analysis

and (ttotal t2) (vm a1) (vm a2).

The above two formulas eliminate the VM and get it.

t, total 2, t2, 2*s, total*(a1, a2), (a1*a2).

Obviously, when t2 is the smallest, t is always the smallest.

The minimum time required for t2 can only be equal to 0, so the minimum time required is t total minimum root number[ 2*s total * (a1 a2) (a1*a2)].

t total shortest root number [ 2 * 1600 * ( sec.

(1) Let the time of acceleration motion t1 and the time of deceleration motion t2, then the time of uniform motion is 130-t1-t2

a1t1=a2t2

t1=a2t2/a1=4t2

Total displacement x=[(130-t1-t2)+130]a2t2 2 is obtained by the above equation t2=2s

vm=a2t2=

2) Accelerate first, then decelerate, and then decelerate until stopped, the shortest time.

At this point there is x=(t1+t2)a2t2 2=1600t2=10s

t1=t=t1+t2=

I think, nn night god, you'd better explain the topic, a1 = meter every square second is the acceleration of starting, then a2 = meter every square second is the acceleration when? Write it down clearly, and maybe someone will answer it for you! @-

b Analysis:

P is placed in the magnetic field of the energized conductor of Mn, the magnetic field of Mn is divided into two parts, the direction of the magnetic field of the upper part of Mn is perpendicular to the paper, and the direction of the magnetic field of the lower part of the Mn is perpendicular to the outside of the paper. Divide P into two parts, although the length of the arc on the top of Mn and the length of the arc on the bottom of Mn are different, they can be regarded as the same equivalent length, but the strength of the magnetic field at the position is different. In this way, according to the left-hand rule, the arc under Mn is stressed in the direction of downward and the magnetic field force is large, while the arc on the upper edge of Mn is stressed in the direction of upward but the magnetic field force is small, and the ring should move downward. 

When the plane falls, it has to go through two states of acceleration and deceleration, otherwise, when it reaches 500m above the ground, the speed will be greater than 10m s = =

According to the formula t=under the root number (2h g), so only find the displacement of the accelerated fall and set the displacement of the acceleration (because only by gravity, that is, the free fall) is h1, and the deceleration is h2, according to the formula v = 2ax under the root number, you can calculate the velocity after falling h1, which is equal to 2gh1 under the root number, the title says that after the displacement of h1 + h2 after falling, the velocity should be less than 10, lz can be imagined, the longer the time required, the greater the time to accelerate and fall, and the more difficult it is to decelerate to 10, So 10 is the cut-off. The title says that it can withstand 2G, so the acceleration of deceleration is 2G

According to the formula v2 square - v1 square = 2ax there is.

100-2gh1=-2*2g*h2

And because h1 + h2 = 5185-500

Can be solved. h1=3125 (h2=1560 leave it alone)t=25s

Hehe, this question is not difficult at all! Why does the landlord call it a physical problem?

This question is of the exact same type as the second question above, but the physical process is different.

Analysis: Obviously, the speed of a free-falling object increases by 10m s every second it passes, and the maximum speed that an airplane can achieve when falling at an altitude of 5000 meters far exceeds the speed required in the question to be no more than 10m s when it is in the air at 500 meters, so it can be seen that the aircraft has gone through two states of motion of first acceleration and then deceleration (I guess the landlord just didn't understand that the plane in this question has gone through these two states of motion).

According to the requirements of the problem, since people can withstand twice the gravitational acceleration at the most, it is required that the acceleration (direction vertical upward) of the aircraft in the process of deceleration is twice the size of the gravitational acceleration, so the equation can be as follows:

h1=gt^2/2

v=gtv^2-(10m/s)^2=2ah2=2*(2g)*h2=4gh2h1+h2=5185m-500m

There are 4 known numbers (h1, h2, t, v) in the above 4 equations, so all roots can be solved. I won't do the specific process of solving the equation, and the landlord can calculate it himself.

Can't you post pictures? I can only rely on my imagination.

1, b2, I can't see the inclined plane of the diagram, if the inclined plane is flat, it is "unchanged"; If it is sunken, it "gradually increases"; If it is convex, "gradually decrease"; If it is uneven, according to the order of the concave and convex surface, just combine it.

3. B, m1, m2 slide at a constant speed, and the force is balanced, and the forces are: "friction force" along the inclined plane, "support force" on the vertical inclined plane, and its own gravity.

The forces of m1 and m2 acting on the triangle are respectively: "friction" along the inclined plane downwards and "pressure" on the perpendicular inclined downward surface. The resultant force of the two forces is the gravitational force of m1 and m2 itself, which is vertically downward, so the triangle is in the horizontal direction and has no force.

2. The size of the search is not ignored, the ball goes up, the rope angle is large, the vertical component of F remains unchanged, the horizontal component increases, and F increases.

FCOSA enlarged.