Middle School Physics Why choose B in 12 questions?

12.Solution: The volume of water drained when the block is in water:

v drainage. m drainage.

Water. 76g/1g/cm3

76 cm3

The volume of alcohol is dislodged when the block is in alcohol:

V row wine. M row wine.

Wine. 64g/

80 cm3

From the analysis of the topic, it can be seen that the block sinks to the bottom in alcohol, and the volume of the block is:

V v row wine.

80 cm3

The block is in water, floating on the surface of the water, and the volume of the exposed part is:

v Lu. v v drainage.

80 cm3

76cm34 cm3

The mass of the block is: m m drainage.

The density of a 76g block is:

m/v＝76g/80 cm3

g cm3kg m3 So, b should be chosen

From the title it follows that the object sinks to the bottom in alcohol, i.e., the volume of the alcohol is equal to the volume of the object.

Volume of discrete alcohol = 64g

Volume of drained water = 76g 1g cm = 76cm When the block is placed in water, v discharges v matter.

Blocks float in the water m row = m matter.

76g/80cm³=

So choose B

This is a multiple-choice question, you can first think that the object is floating in water, at this time: 76g = object v in alcohol, according to Archimedes' principle: f float = g matter =

In the water according to Archimedes' principle: f float = g matter =

Floating alcohol Obviously, the object is sinking in the alcohol, so it belongs to immersion:

64g = object v

v = 64g wine.

Reasons for d wrong:

The density of the same substance can change. Because the state of matter changes, the density changes.

For example, if water turns into ice, the density is small.

Density is rightSpecific volumewithinQualityThe measure of mass, i.e., volume = density. If the mass changes or the volume changes, the density will change, and it has nothing to do with the substance, so d is wrong.

For a simple example, if you stuff a 5-pound quilt into your school bag, it will be very crowded; You stuff it in your suitcase, and it's not as crowded.

The density of the same substance can change.

e.g. water, ice, water vapor. The densities are all different.

But they are the same substance, and the chemical formula is the same, so, d is wrong.

You can simply understand that the liquid, gaseous, solid, and density of objects are all different, and that's fine.

The volume of air can be compressed, and then the density changes.

bAny object has inertia, but there is no push because there is friction.

It can only be pushed if the thrust force is greater than the sliding friction force.

Inertia is related to the mass of the object, and the greater the mass, the greater the inertia.

10A on the energy meter indicates that the maximum allowable current is 10A, not that the current through the energy meter is always 10A, so A is wrong and B is right.

2200W is the maximum total power of the electrical appliances installed in the energy meter, not the rated power of the energy meter.

d.The electrical energy consumed should be 7624 degrees (kWh) and he wrote the wrong unit.

The current on the electric energy meter is the maximum current allowed to pass, P = UI = 220V * 10A = 2200W, 2200W is the maximum total power of the electric power allowed to be installed by the energy meter, so choose B

【b】Correct is certain--- the current through the energy meter can be smaller than 10A, and the maximum allowable passage is 10A. It doesn't work only at 10A.

c] is wrong--- the maximum total power of the electric energy meter allowed to work at the same time is 2200W. The actual total power can be less than 2200W, not only when the total power is 2200W.

220V 10A 50Hz means that the meter works in the power frequency circuit of Chinese mainland 220V 50Hz, and 10A is the maximum allowable current. In addition, the meter basically does not consume energy, 220 * 10 = 2200W refers to the sum of the maximum power of the electrical appliances connected to this meter.

B Yes, the energy meter can only say that the maximum allowable current is 10A, so C is wrong.

Because there is an electric power in the energy meter, but it is very small (generally not more than a few watts), it will not be 2200 W.

The electric energy meter does not have the word "rated power", "rated power" is the power during normal operation, and the electric energy meter, as long as it does not exceed the maximum power it can withstand, is working normally, and the 2200w is the maximum power it can withstand.

The energy meter itself is only a tool for measuring electrical work and does not consume electric energy, so the statement of the rated power of the C energy meter is wrong.

If this nameplate is a machine, C is right. However, the energy meter is a measurement tool that does not have a power rating.

2200W refers to the maximum power value that can be used at the same time for his household appliances.

The C plates were chosen, because they have the same speed, with respect to the fixed ball toss also have the same speed, and as a result, the ship falls into the hand.

Alcohol will vaporize when it heats up! Take it out when you bush warm water! When it gets cold, it liquefies! So the plastic bag will shrink!

Alcohol is heated in hot water and vaporized into gas, which is taken out of the hot water and liquefied into a liquid when it is cold.

When the alcohol went in, it was liquid, and then it was 80, and the bag rose, that is, the liquid state became gas, and then it was taken out, and there was no 80, and it changed from the gas to the liquid state, which was liquefaction.

The boiling point of alcohol is 80, put it in to absorb heat and vaporize, take it out below 80 degrees Celsius, and release it to liquefy.

A and b are the same height, but you can tell that the proportion of alcohol above point B is greater than the proportion of water above point A.

Again, the total mass of the two is the same.

The alcohol above the B is of greater quality.

And both cups are the same.

So the pressure at point B is greater.

Yours is the driving force for me to move forward, if you don't understand, please "ask", I will know everything, hope, thank you.

If there are two identical cylindrical flat-bottomed cups on the tabletop, each containing water and alcohol of equal mass, the pressure of the liquid on the bottom of the container is equal to the gravitational force of the liquid, according to the pressure formula p=f s

It can be seen that the pressure of water and alcohol on the bottom of the container is equal, i.e. water gh water = alcohol gh alcohol;

The distance between points A and B and the bottom of the cup is equal, and it can be seen from the liquid pressure formula P= Gh that the pressure at point A is Pa= water g(h water-h) = water gh water - water gh;

Pressure at point B: Pb = Alcohol g (H Alcohol - H) = Alcohol GH - Alcohol GH;

Can know pa pb

So you should choose B

Code word hard hope thank you、。。

Pressure = mass density.

The mass is constant, the density is inversely proportional to the pressure, and the density of water is greater than that of alcohol, so the pressure of alcohol is stronger than that of water.

Correct answer to the mold bend B

If the object distance is greater than twice the focal length, the real image will be reduced by an inverted handstand, and the object distance will be reduced and the image will become larger, and the speed of the object will be less than the moving speed of the seepage object.

Like getting bigger. You can think of a convex collapsing lens as an eye, like a distant object that is round in a sock approaching. Like nature is getting bigger. As for the change in speed, I regret it and ask for advice.

Let the supply voltage be U and the coil resistance be :

r＝u/i＝u/2

When working normally, the extra power is p, and the amount is ir

Total power power: p ui

Mechanical efficiency: w has w total (p p amount) p (unclear question.)

By the title, the internal resistance of the motor r=u 2

Under normal total power p=ui'=

Extra power p'=i’^2r=……=

Useful power p"=p-p'=……=

Hence =p"/p=……= 70%