This question is the physics question we took today. Could you please help me answer the question!!!

Unreal. This report is true and false, so it is difficult to distinguish.

If the pressure is reduced, the point of water can be lowered, and it can indeed boil at room temperature. (i.e. the ** of the bubble.) ）

However, simply boiling water is unlikely to do anything to clean clothes. At most, it plays the role of washing up at room temperature water, and has no effect on stubborn stains.

By the way, laundry foam is a by-product of washing clothes or soap that breaks the surface tension of the water to absorb fat-soluble stains. By the way, it produces foam. ）

People who think they can wash their clothes with foam are stupid, which is no different from the little broken child who shouts about transformation with an Ultraman transformer.

And, in order to maintain this low-pressure boiling, the washing machine must be completely closed, and water vapor needs to be constantly sucked out (not discharged) from it. Prevent pressure recovery and the water no longer boils. This requires additional energy. The gains outweigh the losses.

It should be possible that if the pressure is close to the vacuum, the water will boil at room temperature.

I wonder where this bubble came from?

Washing powder? If the laundry detergent does not have the effect of washing, is it still laundry detergent?

If the laundry detergent needs to be under pressure to have a washing effect, will you use such a laundry detergent?

Water? Can water create foam?

Is this still water? Hide.

This is impossible, the boiling point of water at normal atmospheric pressure is 100 degrees, if you want to reduce the boiling point, you have to reduce the pressure, but because there is an atmosphere, if you want to reduce the pressure, you must be in a closed environment, and water boiling is actually the process of water from liquid to gaseous, in fact, it increases the total amount of gas in the closed container, that is, a pressurization process, the boiling point of water will also increase, which is the opposite of the conditions we need, so this report is impossible to achieve.

Theoretically, in a vacuum, as long as the water is higher than absolute zero, it can boil, but in fact, as soon as the water boils, the air pressure must rise, and it is not a vacuum.

The reason is due to the different coefficients of expansion of the substances. The glass will expand rapidly when it comes into contact with hot water, so it will cause the liquid column to fall, and then because the expansion coefficient of the liquid column (mercury) is greater than that of the glass, it will soon surpass the glass in the process of continuous expansion, so the liquid column will rise again.

In fact, the liquid column of the thermometer at any time falls first and then rises, but when the temperature change is not very large, this phenomenon is very insignificant and not easy to observe. The drastic temperature change that magnifies the process and makes it easy to observe, on the other hand, is measured at 0 degrees Celsius and immediately placed in hot water.

Personally, I think that it will slowly descend and then start to rise, because the heat transfer process takes time, and the material also has the property of heat storage. In other words, there is a time lag in heat transfer.

27.Solution:

The work done by the object overcoming gravity: wg=mgh=500kg 10m s 20m=100kj

The velocity of an object when it rises to 10m: vt= 2as= 2 From Newton's second law: f-mg=ma, we get: f=m(g+a)=500kg (10ms+

where f is the vertical upward tensile force.

Instantaneous power: P=FVT=5250N

These two physics analysis questions need to be decomposed by the synthesis of forces when calculating, and then they can be judged.

It can probably be seen from ** that these two physical analysis problems need to be decomposed by the synthesis of forces when calculating, and then they can be judged.

1) The ascent and fall times are equal. So the free fall time is 4s, v=gt=10 4=40ms.

ek=1/2×

ep=02) the highest point velocity of the conservation of mechanical energy is 0, ek=0ep=40j

3) When the gravitational potential energy is half of the original in the middle position, the reduced gravitational potential energy is converted into kinetic energy. ek=ep=40/2=20j

From the time it is thrown to the point of landing, it takes 8 seconds, and the ascent and descent times are 4 seconds each.

The initial velocity is v0=gt=10x4=40m s

The kinetic energy when thrown is ek=mv0 2=

When the potential energy is 0 and the highest point of the highest point can be known according to the law of conservation of mechanical energy (or calculate the maximum height reached, and then calculate EP=MGH), the gravitational potential energy is 160J and the kinetic energy is zero.

When reaching half the height, the gravitational potential energy is halved and is 80j, then the kinetic energy is 160-80=80j.

Throwing vertically from the ground, regardless of resistance, you can see the ascent and descent as the opposite process.

One is to convert kinetic energy into potential energy, and the other is to convert potential energy into kinetic energy, and at the highest point, the velocity is zero, the kinetic energy is zero, and the potential energy is maximum. The acceleration of the whole process remains unchanged, the time is 4s respectively, the maximum velocity value is v=at=10*4=40, the kinetic energy is the largest when thrown, e=(m*v*v) 2, and the potential energy is zero. At the highest point, the potential energy is the largest, which is the maximum kinetic energy just now, and the kinetic energy is zero at this time.

The maximum height s=a*t*t 2=10*4*4 2=80m, the ascent is 40 meters, the time is 2 times the root number 2, the speed is 20 times the root number 2, the kinetic energy e=(m*v*v) 2, the potential energy is the maximum kinetic energy minus the kinetic energy at this time.

1. The buoyancy is 10n, because the wooden block is floating, so the buoyancy is equal to the gravity (the wooden block is stationary, it must be subject to the balance force).

2. According to Archimedes' law, the buoyancy of a wooden block is equal to the gravitational force of its water discharge, that is, the buoyancy should be equal to the gravity of water with the same volume as the wooden block 3 4. Let the volume of the block be v, then there is water·3v 4·g=f floating, and v=1 750m is obtained, so the density of the block =g (vg)=

Buoyancy is 10 Newtons.

The density is a quarter of the density of kilograms per cubic meter.

Option B

Pressure p=f s

The pressure is the same, the pressure area of A and B is smaller than the pressure area of B on the ground, so the pressure of A on B is strong but because the mass is the same, so the gravity of A B is the same, so the pressure is the same, I hope it will be useful to you Thank you.

m A=m B, A=4 B, according to v=m, we can know that the mass must be, and the volume is inversely proportional to the density. Because A: B=4:

1, it can be known that v A: v B = 1:4, because V A: in the question

v B = 1:5, so it can be seen that the volume of B is greater than 4v A, that is, the solid volume, so the hollow object is B.

The volume of the hollow part, the solid volume is 4v, and the hollow object volume is 5v, so the volume of the hollow part is: v

If the volume of A is v, then the volume of B is 5v. B density, then A density 4.

Let's use the hypothetical method.

Assuming that both objects are solid, then mass A is 4v and mass B is 5v. A and B should be of equal quality, and only B has a partial hollow to be satisfied.

A is solid, the mass is 4V, and B is 4V. B solid is 5v, solid B removes 1v to become hollow B, let's take the solid B to dig out 1v, the part that is dug is of course hollow. B density, then the excavated part is 1V.

It is to dig out one-fifth of B. The hollow part is 1 5V B.

It's a simple question.