Physics Questions! Please, physics questions! Help!

The first must be the analysis:

According to the minimum take-off speed of the aircraft, the length of the runway and the acceleration that the aircraft can provide:

While gliding 100m (displacement) the final velocity is to be 50m s, while the acceleration is.

Columnar (the computer can't be columnar, so use the text narrative to follow):

The square of the initial velocity minus the square of the final velocity is equal to the square of the negative 2a x.

This is one of the basic formulas of physics, and it is known that any three of the four terms of initial velocity, end velocity, acceleration, and displacement are the formulas for finding the fourth term.

In fact, as long as you sort out the useful information in the question (as above), you will have a clear understanding of the idea of solving the problem.

In any case, you have to isolate each change of motion and list its properties separately (I mean initial and final velocity, acceleration, displacement, time, etc.).

Then calculate the motion of different properties separately, and finally observe the relationship between them, such as the same property and the order in which it occurs, so that all the object motion problems can be easily solved!

The test point of this question is the two formulas of v end = v beginning + at and s = v beginning t + 1 2at 2, acceleration a = , v end = 50, s = 100, bring this number in, and solve the system of equations.

To maximize the landing speed, the horizontal velocity and vertical velocity should be the maximum. Annihilation.

According to the magnitude of the horizontal velocity of the Lee spine, a and d can be excluded

Vertical speed = gt

According to h=1 2gt 2, it can be seen that the higher the height, the longer the time, then v=gt, the greater the speed, so choose c

Yes. If you don't envy the old, you can compare it with this acre. The centripetal force experienced by an object A on the ground = mv 2 r, while the centripetal force of a geostationary satellite in orbit = gmm (r+h) 2

This problem is like this, the time for the straight rod to pass through the cylinder should be the time for the top of the straight rod to leave the bottom of the cylinder minus the time for the low end of the straight rod to reach the upper part of the cylinder, the displacement of the top of the straight rod when it leaves the bottom of the cylinder is 20m, and the displacement of the low end of the straight rod to the upper part of the cylinder is 10m, so using the formula s=(1 2)gt 2, bring in s1=20, s2=10, you can get t1=2 seconds, t2=root number 2 seconds, so the time should be 2-root number 2

From the title, it can be seen that the straight bar ab is a free fall movement.

The timing starts from the short cut of the hanging line, and the time from the lower end of the straight rod to the upper end of the cylinder CD is t1, and the time when the upper end of the straight rod coincides with the lower end of the cylinder CD is t2

It can be known that the falling height in t1 time.

h1=1/2*gt1^2 h1=10mt1=√(2h1/g)=√2s

Drop height in t2 time.

h2=1/2*gt2^2 h2=20mt2=√(2h2/g)=2s

The time it takes for a straight rod to pass through a cylinder CD.

t=t2-t1=2-√2 s

The others are nonsense, not referring to the total time, but to the time when the lower part of the rod begins to enter the cylinder and the top of the rod exits the cylinder

The time for the straight rod to pass through the cylinder should be the time for the top of the straight rod to leave the bottom of the cylinder minus the time for the low end of the straight rod to reach the upper part of the cylinder, the displacement of the top of the straight rod when it leaves the bottom of the cylinder is 20m, and the displacement of the low end of the straight rod to the upper part of the cylinder is 10m, so using the formula s=(1 2)gt 2, bring in s1=20, s2=10, you can get t1=2 seconds, t2=root number 2 seconds, so the time should be 2-root number 2

This is a matter of frame of reference. The title says that the stick is to be "crossed", so the two sides of the frame of reference are the top end of the stick and the lowest end of the circle. Then it becomes that the initial velocity is zero, the acceleration is 10, and the displacement = 5 + 10 + 5 (stick length + spacing + cylinder) = 20, then the time is just fine.

I haven't counted the formula for years and forgot. Don't ask for scores. Hope it helps.

Thereupon. You do it yourself :)

ps。I did the math. I actually remembered the formula. s=vo*t+1 2a*t 2, s=20, vo=0, a=10, and calculate t=2, which is two seconds.

First of all, the motion of the object is determined, which is free fall, and moreover, every point of the rod, is free fall.

Second, through the cylinder. Take the top point of the pole, as long as this point passes through the cylinder, the pole passes through completely. Then, at this point a on the pole, the displacement of motion is, 5 + 10 + 5 = 20m

OK, substitute the formula: 20 = 1 2 x 10 x t x t t = 2 seconds.

The time when the straight rod "passes through the cylinder" = the time when the upper end of ab leaves the lower end of the cylinder t-the time when the lower end of ab touches the upper end of the cylinder t

s=(1/2)gt^2，s=(1/2)gt^2t=(2s/g)^(1/2)=(2*(5+10+5)/10)^(1/2)=2

t=(2s/g)^(1/2)=(2*10/10)^(1/2)=2^(1/2)

t-t=2-2^(1/)=

The time spent is 2s

Calculation process. 1 2at1 2=10 t1=2s At the end of the 2nd second, the lower end of the rod reaches the upper end of the barrel.

1 2at2 2=10+5+5=20 t2=4s At the end of the fourth second, the lower end of the rod passes through the lower end of the barrel.

This process takes 4—2=2s

The easiest way.

Taking b as the research object, the road section it has to pass through is 5+10+5=20, so 1 2gt 2=20 gets t=2

Give me extra points, I'm the easiest.

The landlord used so many reward points, it's too wasteful.

Many physics problems are idealized, and you have to follow the ideas of the original questions to idealize.

When the movement reaches the lowest point, it collides with the block (the collision time is very short), and the distance to the water level when it rises to the highest point is h 16. - That is, the kinetic energy (1 2mv1' squared) is all converted into a potential energy of 16 mgh.

There is a loss of energy at the moment of elastic impact, such as the generation of heat; --The collision time is very short--- which indicates that this is an elastic collision, and you have to follow the idea that energy is not conserved in order to score.

Inelastic collisions are generally conserved in energy (generally considered to be conserved, but certainly not conserved in the strict sense).

According to the method you said, it is wrong, the work w = 1 2mva after the impact of the square of the square - 1 2mva before the impact of the square of the moment of the square of the moment of the impact indicates the amount of change in the kinetic energy of the ball before and after the impact, not due to the work done by gravity, but the result of the impact force. In the event of an impact, the impact force acts for a very short period of time, and the impact force is unknown, so you are not in the right equation.

Draw you a schematic diagram of the structure of a multi-meter, and if you look at the battery installation method inside, you will understand the question you are asking.

In fact, the positive pole of the battery inside the multimeter wants to be connected with the black watch pen, the black watch pen has a high potential, and the negative pole of the battery is connected with the red watch pen, and the red watch pen has a low potential. Therefore, when measuring the unknown resistance, the multimeter is equivalent to a power supply, and the current flows from the black meter pen into the resistance. Resistors flow out of the red pen.

Hope it helps.

Because when measuring the resistance, the positive pole of the battery in the meter is connected to the black watch pen, so the black watch pen is the positive pole and the electric potential is high.

However, this is not the case with the numeric table that is now widely used, with the red watch pen being the positive pole.

The ohmic file of the multi-meter has an internal power supply, and the positive pole is connected to the black watch pen. Remember: the current of a multimeter is always red in and black out.

When measuring resistors for many purposes, the black watch pen is connected to the + stage of the internal power supply, so it is a high potential.

The current flow direction is still from the black pen to the multimeter, from the red pen to the multimeter, and from the black pen to the resistance.

1. The calorific value of alcohol is [.

2. When the car brakes on the highway, the wheels stop rotating, and the surface temperature of the tire will rise sharply to produce smoke and leave black marks on the ground.

3. How many kilograms of alcohol do you need to burn to get the heat to the eighth power?

m=qput q=(。

4. Tell how energy is transformed in the following phenomena.

1) Generator power generation [mechanical energy is converted into electrical energy].

2) Gas expansion does work [internal energy is converted into mechanical energy].

3) Firecrackers take off in the air [chemical energy is converted into internal energy and then converted into mechanical energy].

5. Judgment of true or false: when the object does work externally, its own energy must be reduced. Correct

6. The following statement is correct [a].

a. The temperature of the metal remains unchanged during the melting and solidification of the liquid metal.

b. After the object absorbs heat, the temperature must rise.

c. The boiling point of water in any case is 100 degrees Celsius.

d. The temperature of the ice must be lower than 0 degrees Celsius under any circumstances.

7. The temperature of the object increases, indicating [d].

a. Its internal energy increases, and the heat does not change b. The speed of molecular movement does not change, and the heat increases.

c. The speed of molecular motion remains unchanged, and the internal energy increases d. The speed of molecular motion accelerates, and the internal energy increases.

Answer: When the cap is suddenly opened, the gas in the bottle expands rapidly, and the internal energy is [reduced], the temperature is reduced, and the water vapor near the bottle mouth is cold [liquefied] to form a large number of small water droplets, which is the "white gas" we see.

9. When rinsing Xiaohong**, you need 200 grams of warm water at 40 degrees Celsius. At that time, there were only two kinds of water at 10 degrees Celsius and 90 degrees Celsius at home, so how many grams of each was needed to mix into the water needed? (excluding heat loss).

Solution: Q=cm t represents cold water heat absorption and hot water heat release respectively

Q aspiration = cm1 (40 -10).

q amp = cm2 (90 -40).

Column equations: m1+m2=200g; cm1(40℃-10℃)=cm2(90℃-40℃）。

Solving this system of equations yields: m1 = 125g m2 = 75g

These questions are worth some points, please!

1.This is to find on the Internet, preferably an encyclopedia.

2.Mechanical energy to internal energy.

3.There are values in the textbook, but I don't know.

4.(1) Generator power generation (chemical energy to electrical energy).

2) Gas expansion does work (internal energy is converted into mechanical energy when heat is transferred, and human chemical energy is converted into mechanical energy when work is done).

3) Firecrackers rise in the air (chemical energy is converted into mechanical energy, as well as internal energy) 5False, only if no energy is input.

8.Work is done to reduce condensation.

9.I don't know the exact number for this to be calculated.

1- Check it online, I don't remember either;

2. Mechanical energy is converted into internal energy;

3. Divide the calories by the calories emitted by one kilogram of alcohol;

4. (1) Other energy (such as hydroelectric power is the mechanical energy of water) is converted into electrical energy;

2) Conversion of internal energy into mechanical energy; (The same as the internal combustion engine works).

3) chemical energy is converted into internal energy and then into mechanical energy;

5 to 6, A to , metal is a crystal with a melting point and a boiling point.

bFalse, e.g. water absorbs heat when boiling, but the temperature remains unchanged at 100 degrees Celsius under standard conditions;

c False, it is related to atmospheric pressure, low air pressure and low boiling point in high mountains, and it is not easy to boil eggs;

d false, the temperature of the ice-water mixture is equal to 0 degrees Celsius.

In the 7d pair, temperature is a sign of the average speed of the molecular motion of an object, and the temperature increases, the molecular motion accelerates, and the internal energy increases.

8. Answer: When the cap is opened suddenly, the gas in the bottle expands rapidly, the external (work), the internal energy (decreases), the temperature (decreases), and the water vapor near the bottle mouth is cooled (liquefied) to form a large number of small water droplets, which is the "white gas" we see.

9. Set 10 degrees Celsius water to x grams of 90 degrees Celsius water y grams x + y = 200 ......（1）

Because water at 90 degrees Celsius drops to 40 degrees Celsius to release heat, let the specific heat capacity of the water be c, and the heat released is: (90-40)*x

Because water at 10 degrees Celsius rises to 40 degrees Celsius to absorb heat, let the specific heat capacity of the water be c, and the heat absorption is: (40-10)*y

Hot water transfers heat to cold water, which is conserved by energy: heat released = heat absorbed.

50x=30y（2）

The equation can be solved by the two equations (1) and (2).

1. Place the ball at a low height (denoted as h1) and let it fall and hit the wooden block, which will move at a distance of s1.

2. Place the same ball at a higher height (denoted as h2), repeat the above experiment, and write down the distance moved by the wooden block s2

Because s2 is greater than s1, the kinetic energy of the ball is large in the first experiment, and then look at the first and second experiments, h1