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1. The buoyancy of a small ball with a volume of 2x10 cubic meters and a volume of negative cubic meters is - Niu if it is completely immersed in water. If half of its volume is immersed in water, the buoyancy is - Niu 2. When the gravity of the metal block is 26.5n and the metal block is suspended by a spring scale and immersed in water, the indication of the spring scale is 16.7n. The buoyancy of the metal block under water is - n 3. An object weighing 4 N, with a volume of 0.5 cubic decimeter, will be completely immersed in water, and the buoyancy it receives is - cow, it will lose weight in water—— 4. If a piece of wood weighs 20n and floats on the surface of the water and is still, the buoyancy of the piece of wood to the water is - Niu 5. An ocean going ship sailed into the Huangpu River from the East China Sea. The ship realized the buoyancy it received
1. If half of the volume is immersed in water, F2 = PGV / 2 = 9.8N. 2, buoyancy f = 26.5-16.7 = 9.8n3, buoyancy f = PGV = 4.9n, it will float up in water
The difference between the formula of ρ = GV and the formula of displacement buoyancy F,
That is to say, what kind of situations do they apply to, and why do the two formulas sometimes give different answers?
There is a question about the buoyancy of a ship sailing in the sea. I am wrong to use the former
The former is applicable to any case, note that V is the volume immersed in liquid, and the latter is applicable to floating and suspension, because buoyancy is equal to gravity and cannot be used when sinking to the bottom
A formula for calculating buoyancy
Gravity difference method (weighing method) f floating = G-F (G is the gravity of the object in the air, f is the gravity of the object in the liquid)
2. Formula method (Archimedes principle) f floating = g row = m row g = ρ liquid GV row
3. Floating or suspension condition method: that is, f floating = g floating when floating or suspending
How to find the formula of effective work and general attack of mechanical efficiency?
Is the mechanical efficiency formula of inclined plane the same as that of pulley block
The principle is the same, all are active work / total work, but when the pulley block is used vertically, regardless of friction, the work done to overcome the gravity of the object is active work, and the work done by the tension at the free end of the rope is total work. Inclined plane: the work done by the tension along the inclined plane is total work, and the work done by overcoming the gravity of the object is active work
There are several ways to calculate the mechanical efficiency of pulley block? Just write the formula
In the case of ignoring friction, there are three formulas, but the method is essentially one
Formula 1: η = wyou / wtotal = wyou / (wyou + W amount)
Formula 2: η = wyou / wtotal = GH / Fs, s = NH, n is the number of rope segments
Formula 3: η = wyou / wtotal = g / (G + G)
The essence is: w have / W total
I don't know what to ask
Solving the complete formula of mechanical efficiency, deformation formula and extension formula of pressure in physics mechanics of junior high school
Pressure formula: P = f / s when the object is placed on the horizontal plane, there is no other object acting, its pressure on the horizontal plane = its gravity formula can be written as P = g / S = mg / s deformation formula F = PS, s = f / P when the uniform cylinder or cuboid or cube is placed vertically on the horizontal plane, the formula P = f / S = mg / S = HSPG / S = HPG
Explanation of mechanical efficiency formula of pulley block
Be able to write down the meaning of each letter
Write the formula first
Then write down the meaning of each letter in the formula
η = w have / W total = GH / Fs = g / NF
η = w you / W total = w you / (w you + W extra) = g / (G + G dynamic)
W has: useful work w total: total work G: gravity of object H: height of weight rising
F: The tension at the free end of the rope n: the number of segments of the rope that bear the weight
W extra: extra work g dynamic: gravity of moving pulley
As shown in figure a, it is a crane working on the construction site. The pulley block on the boom (as shown in Figure b) increases the weight of 1.2 × 103kg by 3M vertically and uniformly, and the pull force F is 8000n, then the work done by the pull force F is______ J. The mechanical efficiency of the pulley block is______ ．
It can be seen from the figure that the pulley block is loaded by three sections of rope, so s = 3H = 3 × 3M = 9m; useful work: W useful = GH = MGH = 1.2 × 103kg × 10N / kg × 3M = 3.6 × 104j; total work: W total = FS = 8000n × 9m = 7.2 × 104j; mechanical efficiency: η = w useful, w total × 100% = 3.6 × 104j, 7.2 × 104j × 100% = 50%; so the answer is: 7.2 × 104j; 50%
1. What's the working principle of pulley block? Why can you pull objects up with pulley block? How!
2. There are several sections of rope in the pulley block, and the required tension is a fraction of the weight of the object. But I see that there is only one rope in the diagram of the pulley block. How can it be divided into several sections? How can it be divided? I don't know!
Lever principle
Because the pulley block is against a labor-saving lever, it can pull the object up
This is the number of ropes on the moving pulley. That is to say, the number of ropes on the moving pulley can bear the gravity of the object. The direct way is to see how many ropes on the moving pulley are upward
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- 12. Typical problems in junior high school physics
- 13. Xiaohua did the experiment of "estimating the value of atmospheric pressure." (1) please complete the following experimental steps. A. push the piston of the syringe to the top of the syringe barrel______ Then seal the small hole of the syringe with a rubber cap. B. fasten the neck of the piston of the syringe with a fine nylon rope so that one end of the rope is connected with the hook of the spring dynamometer, and then pull the syringe barrel horizontally and slowly to the right______ Write it down______ It is equal to the pressure of the atmosphere on the piston, F.C______ , denoted as l, read out the volume V of the syringe, then the area s of the piston=______ Finally, the value p of atmospheric pressure at this time is calculated=______ (write the expression with the measured quantity). (2) in the experiment, Xiaohua used the measuring instrument correctly, and the reading was correct, but she found that there was always deviation in the measurement results, which may be caused by (write two points)______ ．
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- 17. buoyancy A and B are liquid and solid respectively. The density of liquid a is 1g / cm3, and that of solid B is 0.5g/cm3. When a solid solid (composed of substance B) with a volume of 10-3m3 is put into a container containing enough liquid of substance A, how much buoyancy does the solid solid receive when it is still? How much volume does the liquid displace?
- 18. In a bathing beach, the bottom of the water is full of stones. In the process of swimming from deep water to shallow water, the following experience and analysis are reasonable () A. Feet are getting more and more painful because water has less and less support for people. B. feet are getting more and more painful because people are receiving more and more gravity. C. feet don't hurt because people are getting lighter and lighter. D. feet don't hurt because water has more and more support for people
- 19. Who listed the related formulas of physical pressure and buoyancy one by one, including Rou = m / V, which is not published in textbooks? Don't take too many words to explain in front of me. Just tell me what the physical quantity is. I want to copy and paste it
- 20. A course of junior high school physics [pressure and buoyancy], This is the physical simulation of Haidian District in Beijing in 2009 As shown in the figure (a cylindrical container contains a plastic box, in which an iron block floats on the water surface), the cylindrical container with bottom area S1 contains liquid with unknown density. Put a cube metal block with density ρ into the rectangular plastic box with bottom area S2 (the thickness of the plastic box can be ignored), The plastic box floats on the liquid surface (the liquid will not overflow the container), and its immersion depth is H1. If the metal block is taken out of the plastic box, it is tied under the plastic box with thin wire, and put into the liquid, the metal block does not contact the container, and the immersion depth of the plastic box is H2. Cut the thin wire, the metal block will sink to the bottom of the container, and the plastic box floats on the liquid surface, The depth of immersion is H3. If the plastic box is always upright without inclination, the pressure of the liquid on the bottom of the cylindrical container is reduced before and after the thin line is cut? Two supplementary points: 1. The density of the liquid in the container is unknown, and the expression should not contain ρ liquid. 2. The question is how much pressure has been reduced. Not why.