Physics questions, ask a few questions, thank you for your help in the emergency!!!!!!

I miss you very much, these questions are not difficult, but I use a mobile phone, I can't see the picture, I'm so embarrassed....

1, the sum of G2 and G1 and the buoyancy balance with air.

2, c, are 120 degrees to be able to balance.

3. The question is not clear.

4, b, the end of the displacement increase is not a=0

The end of the decrease in c and v is not a=0, and there will be an increase in the opposite direction.

1.Because there are two ends of the cable, one end acts on G1 and the other end acts on G2, so that it can be straightened, and the upward force only acts on G2, and the downward pull force on G1 balances with the resistance of the parachute.

2.I don't understand the meaning. Does Khan have a picture?

3.The resultant force is indeed gravity, but the pulling force of each line is changing, o does not change, ab is far away, sin changes, so the tension force should become larger, and the horizontal direction is canceled.

4.It's impossible to stop the increase in displacement.,C I think it's possible, but it shouldn't be in line with the meaning of the question.。

Supplement 1, the person is subject to buoyancy (resistance), the force of the person is the resistance, the pull of the line, and the gravity. The parachute is subjected to gravity, drag, and downward pull of the line.

And the line is also subjected to two forces, up and down, which should be the same.

People and umbrellas should be analyzed separately, not as a whole.

It seems that the umbrella pulls the person, but because of the maintenance of the rope. Both have their own force relationships.

1.I think this question should be specific. For a person, the force is balanced, and the pulling force is equal to its gravitational force. People are not subject to buoyancy, and the balance with the parachute is air resistance. Not the so-called buoyancy.

The three forces are balanced and equal.

3.I feel like you're missing a diagram for this question.

AB gradually moves away, which means that every point is balanced by force during the movement. Do an orthogonal decomposition.

AB is far away, the angle becomes larger, both forces change, but the net force in the vertical direction remains unchanged, initially FA=0, FB=G, after pulling away, FA has been increasing, FB first becomes smaller and then larger.

4.I feel that the acceleration implied in the question is positive, otherwise if it is negative, it will not be able to be clearly distinguished, so I choose AD

1.We can't all look at things in a holistic way. First you isolate people. People are at a constant speed, so the force is balanced, and the above formula is fine.

At the same time, the parachute is also balanced, it is affected by gravity, the downward pull of the rope, it seems to be unbalanced, in fact you ignore the most important force of skydiving: buoyancy.

2.It should be c, it's not good to draw a picture, you can draw a picture of this.

3.You're right, but there's one word you don't notice: gradually moving away. This word determines that the object is always in equilibrium. Then orthogonal decomposition, it can be solved.

4.The acceleration is constantly decreasing, which means that the absolute value is decreasing. You say that acceleration is negative, but you don't know that the symbol represents the direction and not the magnitude. It asks about size, like asking you about uniform circular motion.

The speed is the same, understand?

1 Obviously, the parachute is balanced, and its forces are as follows: cable pull, air resistance, and its own gravity. But how do you calculate air resistance?

In the case of the pull wire, its pull on the person is in the opposite direction equal to the amount of the pull force on the parachute, so the problem is solved by analyzing the force on the person, because the person is subjected to gravity and pull (the air buoyancy and drag are ignored because the air density is too small and the person is not moving too fast).

2 C should be selected for drawing analysis

The third question: Is there a lack of pictures?

4 In general, unless otherwise specified, the original velocity direction is considered to be positive.

Skydivers are subjected to gravity, the resistance of the air, the buoyancy of the parachute.

The parachute is subject to the pull of the skydiver, gravity, resistance of the air.

Both are balanced by force, so the speed plummets.

The resistance of the air, the buoyancy of the parachute, the gravitational force of the skydiver and the parachute.

1.Human analysis: the tensile equilibrium of g1 on the line; For the analysis of the umbrella, G2, the linear tension and the air resistance are balanced.

2.I didn't understand the question, can you give a picture a ...... first

The magnitude and direction of fb have changed, the force is a vector, obeying the vector synthesis, and it is still possible to balance the resultant force of fa and fb with gravity after the distance becomes larger;

4.Since the initial state is unknown, if the question only gives these conditions, BC is indeed right. c, a and v0 can be reversed.

PS: What I don't quite understand is, what is the difference between b and d?

1 person and the umbrella fall at a uniform speed, so the gravity of the person and the pull of the umbrella on the person are two forces balanced. The umbrella is resisted by the air and the two forces are balanced. So it's one twelve.

2 Frankly. I don't get it. sorry!I guess I want to draw a picture.

3 Yes. 4. Since it is acceleration, the velocity must increase. During this time, there has been traveling, so the distance increases, and the displacement is a vector with a direction, I am not sure whether to choose D or not. Otherwise, C

The calorific value of anthracite is the power joule.

The specific heat of water is 4200

10 liters of water is generally 10 kilograms.

The water temperature can rise up to 100

XKG anthracite is required.

100-20）*10*4200=x( 10%x=1kg

This requires you to explain the relationship between force and movement.

What you call eccentric motion is a type of curvilinear motion. When an object is moving in a curvilinear motion, its velocity changes with time. Velocity is a vector quantity, including magnitude and direction.

As long as the velocity vector changes with time, the object must be subjected to a resultant force that is not zero.

According to Newton's second law, f=ma, a and f are vectors, and they also include magnitude and direction. a is the acceleration, which is the rate of change of velocity with time. The rate of change here refers not only to size, but also to direction.

For example, an object moving in a uniform circular motion must be subjected to a centripetal force of constant magnitude, and the direction of this centripetal force is constantly changing. It is emphasized here that the force f is responsible for the change in velocity. The direction of the combined external force at any time can be decomposed into two parts, parallel and perpendicular to the direction of motion of the object, the parallel component changes the magnitude of the velocity, and the perpendicular component changes the direction of velocity.

And f is the gravitational force of the earth on the spacecraft, if the velocity of the spacecraft is constant, then it must move in a uniform circular motion when only the force of the earth is considered on it. Between the first cosmic velocity and the second cosmic velocity, the motion of the spacecraft in an elliptical orbit is calculated by combining the law of conservation of energy, but it will not occur in the uniform elliptical motion you envisioned. Because the gravitational force is not perpendicular to the direction of velocity at any time except perigee and apogee, the velocity of the spacecraft must change, and the closer it is to the Earth, the faster it becomes.

If the universe consists only of the Earth and the spacecraft, the spacecraft will still orbit the Earth even if it exceeds the second cosmic velocity. However, because of the existence of other bodies such as the sun, when the trajectory of the spacecraft is far away from the earth within a certain range, its dominant role will be the gravitational effect of other stars on the spacecraft, and it will gradually move away from the earth.

Basically correct.

Correcting a few mistakes:

1。The speed of planetary motion is not right between the first cosmic velocity and the second cosmic velocity, and should be greater than the second cosmic velocity.

2。The magnitude of the velocity of motion on an elliptical orbit is not constant, the apogee velocity is small, and the perigee velocity is large. The spacecraft draws a line segment with the Earth, and the area swept by the line segment per unit time is equal.

3。The second half of "the gravitational force received is too small, and the gravitational force required is too great" should be changed to maintain the centripetal force greater than the gravitational force required to maintain the orbital motion.

By the way, your comprehension skills are good.

Spacecraft should also have an inertial element.

The higher the temperature, the higher the air pressure, and of course you can't compare the different layers of air in the atmosphere.

When we talk about the relationship between temperature and pressure, we must first define a fixed object, for example, a certain volume of air, and then discuss the relationship between temperature and pressure.

Temperature is actually a measure of the degree of molecular activity, the higher the temperature, the higher the degree of molecular activity, the more molecules hit a plane (this plane can be assumed, it can also be a physical surface of an object) in a unit of time, the greater the force on this plane, and this force is pressure. The pressure per unit area is the pressure.

If it is geographical, the higher the temperature, the lower the air pressure.

I don't know if you're talking about meteorology or physics.

In the case of meteorology, there is no significant relationship between air pressure and temperature. It's just about height.

In physics, the air pressure is proportional to the temperature when the volume is constant, the higher the temperature, the higher the pressure, because the air pressure is caused by the irregular movement of gas molecules hitting the container wall, the higher the temperature, the stronger the irregular movement, and the greater the pressure.

Ideal gas formula PV t = quantitative.

High, the gas expands after heating, and if other factors remain the same, the pressure will rise, isn't this the case with household pressure cookers.