A few problems in physics, a few problems in physics

Categories: Education Science >> Admission >> College Entrance Examination Problem Description:

1Why should pressure cookers be made of aluminum?

2. Why should a pressure limiting valve be added to the center hole when using?

3. Why should the disfigured sheet in the soluble pores be made of the material with the melting point bottom?

4. The bottom surface of the aluminum kettle used to boil water has several uneven concentric circles Why?

Analysis: 1In addition to ductility, an oxide film is formed on the surface of aluminum, which protects the metal.

2.Control the pressure in the pot, when the pressure increases to a certain value, the valve is pushed up to deflate to prevent the pressure from being too high or too low.

3.When the air hole of the pressure limiting valve is blocked, the pressure increases, and the fusible sheet can be flushed out to ensure safety.

4.Increasing the pressure resistance can also prevent the deformation of the pot body caused by uneven heating of the bottom.

1. The buoyancy will not change, when floating, the buoyancy is equal to the gravity, and the state of the ship floating from the sea into the river is also unchanged, so the displacement is still equal to the gravity of the ship.

2. When the submarine surfaces, it is afloat, and the buoyancy is equal to the gravity of the submarine; When a submarine sinks into the water, it experiences buoyancy equal to the gravitational force of the water equal to its volume. Because analyzing the state of the submarine, it can be seen that when it floats quietly on the surface of the water, is suspended in the water, or rises or falls at a uniform speed in the water, the net external force it is subjected to is actually zero, that is, its buoyancy is equal to its own gravity (don't forget, when the submarine is constantly adding water to the cabin, its own gravity is constantly increasing). When the submarine accelerates and sinks or accelerates its descent, the net external force it is subjected to is not 0, and if it accelerates and sinks, it is the net external force downward, and the buoyancy force is less than the gravitational force; Conversely, an accelerated ascent means that the buoyancy is greater than the gravitational force.

1.If the weight of the ship remains the same, the buoyancy remains the same; The displacement (the weight of the drained water) remains the same. Entering the river from the sea, the density of the water decreases, and the volume of the discharged water increases.

2.In the ascent, the buoyancy is greater than the gravity, that is, a certain amount of water is discharged, reducing the gravity; When diving, buoyancy is less than gravity, that is, a certain amount of water is added, and gravity is increased; When stationary or horizontally navigating in water, buoyancy is equal to gravity; When, in general, submerged in water, the volume of the submarine does not change, the magnitude of buoyancy does not change. Only when it comes to the surface, the buoyancy decreases.

Because buoyancy is equal to gravity, the buoyancy of a ship entering the river from the sea remains the same, but the displacement (which can be understood as the volume of the hull below the surface of the water) increases, because the density of the sea water is greater than that of the river.

1. The buoyancy remains unchanged and the displacement increases, because the density of seawater is greater than that of river water;

2. The buoyancy is greater than the gravity when the submarine floats, and the opposite is when the submarine sinks, and the buoyancy is equal to the gravity when it advances horizontally.

1. The mass of the bottle is m, and the volume is v

M oil + M = 1100g

m water + m = 1260g

So. p oil v+m=

p water v+m =

The substitution density is:

800v+m=

1000v+m=

To solve this system of equations there is.

m=v=cubic meters.

2. The volume of water (which is also the volume of the bottle).

v m water p water (cubic meters.)

The mass of the measured liquid is M liquid

Measure the density of the liquid :p liquid m liquid v cubic meter.

Suppose the volume of the bottle is x, the density of kerosene I don't remember assuming a, and the density of water is 1g cm3

a*x-1*x=1100-1260

This can be used to calculate the volume of the bottle and then substitute it.

The mass of the bottle = 1260-1*x

2 questions. (is the mass of the liquid, (is the volume of the bottle.)

1.The construction of water conservancy projects has seriously disrupted the water cycle in the basin, and the builders lack awareness of this, so they have not taken the initiative to take measures to avoid or mitigate these adverse effects, let alone actively take measures for ecological restoration and compensation. As a result, the ecosystem of the basin deteriorates rapidly after a large number of hydraulic projects are built in the basin.

Second, many river basins adopt cascade development and rolling development, and the capacity of reservoirs even exceeds the annual average runoff of the river basin, resulting in obvious and irreversible ecosystem damage in the river basin. For example, the river flow in the lower reaches of the basin is cut off, and a large number of dewatered river sections appear in the downstream of the diversion power station, which is devastating to the river ecosystem.

Generally speaking, the construction of water conservancy projects has a negative impact on the water cycle of the basin and affects the ecosystem of the basin, and these impacts have the following four aspects: the nodeization of the water cycle in the basin; short-circuiting of the water cycle in the basin; insulating the water cycle in the basin; Isolation of watershed ecosystems.

2.The pipes in the solar water tank are spiral-shaped and help absorb sunlight.

3.I haven't heard of a "fruit" that can be eaten and used as a battery yet, but it is estimated that it will be developed in the future!

1.It is true that the speed at which sound travels in a medium varies from medium to medium.

2.The binaural effect cannot determine the distance of a sound source, because the binaural effect can only determine the position (direction) of a sound source based on the time difference between the sound waves received by both ears. The distance of the sound source must be judged by the strength of the sound source received by both ears.

Right. OK. Binaural effect.

The so-called binaural effect refers to the difference in the distance between the sound source and the left ear when the sound source is biased to the left or right ear, that is, when it deviates from the central axis in front of the two ears, there is a difference in the distance between the sound source and the right ear, which will lead to a difference in the intensity, time and phase of the sound reaching the two ears. This small difference is perceived by the human ear, transmitted to the brain, and compared and analyzed with the auditory experience stored in the brain, the position of the sound is determined, which is the binaural effect.

People use the "binaural effect" to invent stereo technology, and cooperate with electroacoustic equipment to better present various sounds (such as the direct sound of the band performance, the reflection sound of the wall, the spatial distribution of the reverberation sound of the hall, etc.), and there is an immersive "three-dimensional" space feeling. The usual practice of "two-channel stereo" is to use the left and right microphones representing the human ears to receive sound from two directions at the same time, and after the amplification of two sets of amplifiers, it is released from the two speakers at a certain distance from the left and right. It makes people hear different sounds in different directions in both ears, and produces a "three-dimensional" sense of orientation.

I'm a teacher, thank you.

Sound can no longer travel in a vacuum;

The propagation velocity in other media is the fastest among solids and the slowest in gases.

The binaural effect can determine not only the direction of the sound source, but also the distance of the sound source to a certain extent.