On the relationship between buoyancy and knowledge in grade two of junior high school Pilkington, a famous glass manufacturer, was inspired by the uniform distribution of oil droplets on the water surface and invented the "float flat glass" process. The key to the process is to find a solution that can float the glass, and the density of the solution should be less than 1________ (fill in "greater than", "less than" or "equal to") the density of the glass; if a piece of condensed glass is 2 m long, 1 m wide, 5 mm thick, and the density is 2.5 × 103 kg / m3, the mass of the glass is________ kg.

On the relationship between buoyancy and knowledge in grade two of junior high school Pilkington, a famous glass manufacturer, was inspired by the uniform distribution of oil droplets on the water surface and invented the "float flat glass" process. The key to the process is to find a solution that can float the glass, and the density of the solution should be less than 1________ (fill in "greater than", "less than" or "equal to") the density of the glass; if a piece of condensed glass is 2 m long, 1 m wide, 5 mm thick, and the density is 2.5 × 103 kg / m3, the mass of the glass is________ kg.

The density of this solution should be__ Greater than__ (fill in "greater than", "less than" or "equal to") the density of the glass
If a piece of condensed glass is 2 m in length, 1 m in width, 5 mm in thickness and 2.5 × 103 kg / m3 in density, the mass of the glass is
_ 25【m=ρV=2.5*10^3*2*1*0.005=25】_______ kg.
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Buoyancy knowledge of grade two
1. When floating or levitating, why is buoyancy equal to gravity?
2. Floating at any position in the water, buoyancy = gravity. But it doesn't mean that when an object sinks to the bottom, gravity is greater than buoyancy
3. When floating on the water, buoyancy = gravity, doesn't it mean that buoyancy is greater than gravity when the object is floating on the water?
Hurry! Help me!

1. If the two forces are not equal, the object will move, because there is no motion, so the force is equivalent. 2. Sinking to the bottom does not necessarily mean that the gravity is greater than the buoyancy

For example, the buoyancy of an object in water is F1, the volume of water entering is 1 / 2, and the volume of another liquid entering is 2 / 3. If the density of water is known, the density of another liquid can be calculated

Floating
Ψ g = ρ water * g * V row 1 = ρ liquid * g * V row 2
∵ V row 1: V row 2 = 1 / 2:2 / 3 = 3:4
So ρ liquid = 3 / 4, ρ water = 0.75 * 10 cubic kg / m3

Physical knowledge of buoyancy
When buoyancy equals gravity, is the object floating or floating?
Be more specific

When an object floats in water or on the surface of water, its buoyancy will be equal to gravity, because if not, the object will sink or rise under gravity

There is a certain amount of water in the cylindrical container, and the bottom area of the container is s = 50 square centimeter. A piece of ice containing debris is just suspended when it is put into the water. At this time, the rising height of water surface is △ H = 6.4cm. When the ice is melted, the change of water surface height before melting is △ h2 = 0.44cm (1). Calculate the gravity of pure ice g ice (2). Calculate the weight of debris g miscellaneous (3). Calculate the density of debris (G is 10N / kg)

This problem is still difficult, if the relationship between buoyancy and pressure is not fully understood, it is difficult to do it
(1) The density of pure ice is 0.9g/cm ^ 3, otherwise it can't be solved. According to the meaning of the problem, the water surface decreases by 0.44cm ^ 3 after the ice melts into water, that is, the volume of the whole container decreases by s * △ h2 = 22cm ^ 3. In other words, the volume decreases by 22cm ^ 3 after the ice melts into water, If the mass of water is m ice, the volume of water is m ice / ρ water,
(m ice / ρ ice) - (m ice / ρ water) = 22cm ^ 3
When ρ ice = 0.9g/cm ^ 3, ρ water = 1g / cm ^ 3, m ice = 198g, then G ice = 1.98n
(2) According to the meaning of the title, after the ice containing impurities is put in, the rising height of the water surface is △ H = 6.4cm, then it can be seen that the V row generated after the ice is put in = s * △ H = 320cm ^ 3, then the buoyancy F of the impurities and the ice as a whole is floating = ρ water GV row = 3.2n, because the ice containing impurities is just suspended, so the buoyancy is equal to gravity, that is, the total gravity of pure ice and impurities is 3.2n
G ICE + G impurity = 3.2n
Then G = 3.2n-1.98n = 1.22n
(3) According to the suspension, we can know that the average density of ice with impurities should be equal to the density of water, and the density of ice is less than that of water. Therefore, the density of impurities must be greater than that of water. Therefore, when the ice melts, the impurities should sink to the bottom. Therefore, compared with before melting, the water surface should be reduced. According to the theme, the height of water surface reduction is △ h2 = 0.44cm
If the water and impurities melted by ice are still regarded as a whole, now, the water melted by ice can be considered as floating in the original water. The buoyancy of this part of water is equal to its gravity, which is equal to the gravity of ice g ice, and the buoyancy of impurities is lower than its own gravity. Suppose the buoyancy of impurities is f, obviously g ICE + G impurity > G ICE + F
Before and after melting, the buoyancy of ice and impurity is the sum of their total gravity, that is, G ICE + G impurity = 3.2n. After melting, the water and impurity are regarded as a whole, and the buoyancy of ice and impurity is g ICE + F

The speed of a ship is 36km / h in still water. When the ship goes upstream in the river and passes a bridge, a wooden box on the ship is accidentally bumped into the water (after falling into the water, the speed of the wooden box is the same as that of the current). After two minutes, the personnel on the ship find that they immediately turn the bow to catch up with the wooden box, and catch up with the wooden box 600m away from the bridge. What is the water velocity?

Taking the river as the reference, the river is still, and the water tank falls into the water and remains still. The speed of the ship relative to the river is 36km / h in both upstream and downstream. Therefore, the time for the ship to catch up with the wooden box is equal to the time from the wooden box falling into the water to the discovery, that is, 2min = 120s, so the wooden box falling into the water drifting time is t = 120s + 120s = 240s, and the drifting distance is s = 600m. The wooden box drifting speed is the water flow velocity : v = st = 600m240s = 2.5m/s. A: the water velocity is 2.5m/s

If "300r / kW. H" is marked on the electric energy meter, the rotary table of the electric energy meter turns 1 turn, and the electric energy consumed by the electric appliances in the circuit is J. now Xiaohong uses the electric energy meter to calculate the electric power of the electric heating wife at home. When the heater works alone, the electric power of the electric energy meter turns 60 turns within 90s, and the electric power of the heater is w

1.1000*3600/300=12000J
2.（1000*3600/300）*60/90=8kw
There seems to be something wrong with the data of the building owner. The normal electric energy meter should be "3000 R / kW. H"
If so
That's 1200 J and 800 W

Is the light bulb always hindering the power supply? Is there any special situation? I have done a question, but the power supply can flow from the consumer first. What's the matter?

Every kind of object has an obstacle to the power supply, but the size of the obstacle is different. If the electric appliance and the light bulb are connected in series and close to the power supply, it is through the electric appliance first and then through the light bulb

An energy-saving fluorescent lamp with a power of only 11W has the same brightness as a 60W incandescent lamp. If the lamp is on for 5h every day and 30 days in a month, how much energy can this energy-saving lamp save compared with the incandescent lamp in a normal month?

One month power consumption of 60W incandescent lamp = 60 / 1000 kW × (5H × 30) = 9kwh
One month power consumption of 11W energy-saving fluorescent lamp = 11 / 1000kW × (5H × 30) = 1.65kwh
Therefore, the saved electric energy = 9kwh-1.65kwh = 7.35kwh, i.e. 7.35kwh

A question about sound in physics,
A car runs towards a high mountain with a uniform straight-line speed of 10m / s. when it whistles towards the high mountain, it hears the echo after 4 s. calculate the distance between the car and the high mountain when it hears the echo

Suppose the distance between the echo and the mountain is s, then the distance of the sound in 4S is s + (s + 4 * 10) = 340 * 4
S = 660