Several junior high school physics problems, judgment Seek detailed explanations from masters.

If the object is in equilibrium, i.e., at rest or in a uniform linear motion, the resultant force of all the forces experienced by the object is zero, then these forces are called equilibrium forces. The first one is correct.

The heat of an object is only the heat energy transferred in the heat transfer, so it is the amount of change, and it cannot be said: how much, how much is contained. The second error.

The free sliding of an object refers to the change of the state of motion, the reason for the change of the state of motion is force, here it is gravity that makes it slide freely, and inertia has nothing to do with the state of motion. The third question is wrong.

It must be a kilogram.

It is wrong to ask that the slower and slower state of the football is a change in the state of motion, because of the change in the state of motion caused by friction, and the force is the cause of the change in the state of motion, not the reason for maintaining the state of motion.

The first one is correct, it is in equilibrium, and all the forces that are subjected are equilibrium forces.

Wrong.. Calories are the amount of the process, and it cannot be said how much heat is contained.

The ability to slide is the effect of gravity.

Unit mass is not a certain mass.

No, it's getting slower and slower because of friction.

1 True Because being at rest i.e. in equilibrium, all the forces that are exerted are balanced, and only two forces are received, then the two forces are balanced.

2 False You can take the example of crystal boiling, the internal energy increases, and the temperature does not change.

3 False: Because the slide of an object is due to gravity.

4. False: From the unit of specific heat capacity, it can be seen that the heat absorbed by a certain substance is raised by one degree Celsius per kilogram, which is called the specific heat capacity of this substance.

5 False: From Newton's first law, it is known that force is not what sustains the motion of an object.

1. Correct. 2. Incorrect.

3. Incorrect.

4. Incorrect.

5. Incorrect.

All wrong. 1。These two forces are equal in magnitude but not in balance. 5。Indicate that there is resistance.

1 Rape is a measuring tool that can hold a certain weight of something, the density of oil is smaller than that of soy sauce, and the volume of soy sauce of the same quality is smaller than the volume of oil, so the volume of oil measured with soy sauce grape will become smaller, so it is a loss. 2. First measure the mass of the cup and then measure the weight of the cup filled with water, then you can find the volume of the cup, and then measure the weight of the filled oil to find the density. Because it's written on a mobile phone, you can't be too detailed, so you can summarize the steps yourself.

3 Benefits: Abnormal expansion leads to the freezing of the lake surface in winter, not all of it, so that the fish can survive and do not affect the aquaculture industry

1.You've ever seen a bamboo tube for holding water, a stainless steel tool with a vertical handle at the lower end that resembles a bamboo tube that can hold water. The density of oil is smaller than that of water, so it is smaller than soy sauce, and the volume of soy sauce of the same mass is smaller than the volume of oil, so the volume of grape oil of soy sauce will become smaller, so it is a loss.

2.Weigh out the mass of the empty bottle m1

Fill the empty bottle with water and weigh the mass m2

Pour out the water, fill it with soy sauce and weigh out the mass m3

Calculate(m2-m1) (m3-m1)= water v soy sauce v, i.e. soy sauce = (m3-m1) water (m2-m1).

3.The benefits of the paradoxical expansion of water: The large number of glaciers floating on the Arctic water stores large quantities of fresh water for human survival.

Disadvantages: An airtight container filled with water can break when it freezes, e.g. a beer bottle cannot be frozen.

1.First of all, temperature is a macroscopic representation of the intensity of the particle's motion, and the velocity of the particles in an object is normally distributed. Evaporation, on the other hand, is a macroscopic manifestation of water molecules escaping their molecular forces and spilling into the air.

The higher the temperature, the greater the overall velocity of the particles, the greater the possibility of getting rid of the molecular force, so the faster it evaporates, the more heat it takes away, so the temperature curve is generally logarithmic curve.

2.If boiling water is poured on ice, and the boiling water and ice are regarded as the same system, the particle velocity does not conform to the normal distribution, and the particle velocity of the whole system tends to a normal distribution, that is, the ice will absorb heat and melt, while the temperature of the boiling water will drop. In fact, in this process, the velocity of the molecules in the ice also decreases, but in general its velocity increases, so macroscopically the solid ice melts into water that is more atomically free.

3.In fact, if a person lifts an object and does not move at all, he will not be able to do work and will not be tired. But this is not possible, the human body and even all animals are in a constant shaking and shaking.

It's like if you put a pen on your finger, the pen will keep swinging, and the person's standing will also keep swinging like this, but the human cerebellum will constantly correct the person's posture in a small area, so that the person will stand, and the person with an injured cerebellum can't stand because of the lack of correction function. It's the same with the rest of the locomotor system, when you maintain a pose, each part of the body is constantly swaying and vibrating with the joints as fulcrums. In this process, the center of gravity of the object and each part of the human body moves in a three-dimensional space, and the work is constantly done, resulting in tiredness.

The chemical energy consumed is converted into kinetic energy and heat energy for muscle contraction, which in turn is continuously converted in the process of modifying posture and finally converted into heat and lost.

The speed of evaporation is related to temperature, the higher the temperature, the faster the evaporation, and the more heat is taken away, but the evaporation caused by the increase in temperature is not as good as the effect of evaporation and cooling at room temperature.

Boiling water is poured over the ice, and the ice absorbs heat and begins to melt before finally raising the temperature. Ice cubes only cool down when they are heated.

This problem is the definition of work done in physics, that is, work in the physical sense, which is essentially different from the "work" in our life, in physics, as long as you do not meet the two necessary conditions for doing work, even if you are tired and lie down, you do not do work on objects. It has nothing to do with whether or not energy is consumed!

"It is known that the evaporation of water takes away heat, and the hotter the water evaporates, the faster, but can it be said that the hotter the water takes away more heat in the same amount of time? ”

The evaporation of water, including the evaporation of other liquids, in addition to temperature, is also due to other factors:

One is the evaporation area, the larger the area, the faster the evaporation;

the second is temperature, the higher the temperature, the more active, the faster the evaporation;

The third is the gas content of the evaporated substances in the adjacent evaporable space, such as water, the smaller the relative humidity of the space, the easier it is to evaporate;

Some people may also mention the surface airflow, in fact, in essence, the content of the evaporated substances in the air determines the speed of evaporation.

When the content is high enough to a certain extent, it is saturated and no longer evaporates.

Why does pouring boiling water on ice not lower the temperature of the ice, but melting? ”

The melting point of ice is zero, which means that the temperature of ice is high to zero degrees, and if it is heated again, it will not be able to remain solid, it will melt, and it will turn into water before it can continue to heat up.

The boiling point of water is 100 degrees, which means that water begins to vaporize when it reaches 100 degrees Celsius, and it can only continue to heat up after it becomes water vapor.

This is the three-state transformation characteristic of matter: solid, liquid, and gas.

People do not move after lifting objects, they do not do work on objects, but after a long time, they will get tired, and chemical energy will be consumed in their bodies. ”

People don't move after lifting an object, they don't do work on the object, but they are exerting force, maintaining balance, how do people exert themselves? It depends on the tension of the muscles, and maintaining this tension consumes chemical energy.

This chemical energy is consumed, and it is not converted into kinetic energy, potential energy and other mechanical energy, but will be converted into heat energy and dissipated.

Even when the human body is doing work in heavy lifting, a large part of the chemical energy is also dissipated by heat energy, and its efficiency is not very high.

To answer the latter first, when a person lifts an object without moving, no chemical energy is converted into kinetic energy because there is no object motion. Whether work is done on an object or not is only seen if displacement has occurred over a period of time. The chemical energy expended in the human body is converted into the gravitational potential energy of the object.

The amount of heat taken away by water in the same amount of time is related to the internal energy of the water and has nothing to do with heat.

The temperature of the ice does not decrease because the temperature is a measure of the average kinetic energy of the water molecules, not the heat. It is because the ice absorbs heat that its state changes.

No, it depends on what temperature the object takes away the heat, for example, 70° water takes away the heat of the 50° object, but the water transfers heat to it.

..The maximum temperature of ice is 0°, and it is impossible for you to pour water on it for 1° ice because the object is not moving, w=fs, because it is not moving, so it cannot be said that chemical energy is converted into kinetic energy.

I don't know where the energy goes.

1. The higher the temperature, the more heat water takes away in the same amount of time... However, when the water temperature reaches 100, it will no longer heat up.

2 Because when boiling water is poured on ice, first of all, the temperature of the ice is lower than that of boiling water, so the ice will absorb the temperature of the boiling water, and then when the boiling water is poured on the ice, there will be water vapor, and the vapor will liquefy when it meets the ice, and the liquefaction will release heat. Also, when the ice melts and when it vaporizes, it takes away very little heat, so it absorbs more heat than it does with it, so it melts.

3 i`m so i`m afried i can`t do.

The higher the temperature, the more evaporation of molecules per unit of time, because the evaporation of molecules requires a certain amount of heat. So the higher the temperature, the faster the heat is taken away. When ice melts, it absorbs heat, but the temperature does not change.

When a person lifts something, the muscles are contracted, which requires energy. Energy is converted into heat energy and elastic potential energy for muscle contraction.

According to the formula w=cmt, the first problem is no, because the object does not increase the gravitational potential energy or kinetic energy, and the energy goes to more places, such as your body gets hotter.

Energy does not disappear out of thin air, nor does it arise out of thin air, it only transfers energy, so as to achieve equilibrium, water vapor, which looks at the water molecule as an object, it gets energy at room temperature and then evaporates, and then releases energy into the air, and then becomes water This is the formation of rain, which will deice when the bottom of the water is at room temperature. System energy balance.

1: No, you cannot.

2: I think that ice has no thermal conductivity.

3: The metabolism of the human body itself is the conversion of energy, which you can see as the conversion of internal energy.

Actually, I know, but I'm not going to tell you.

Because the distance between the center of the Maldives is 1500km, and because the speed of the tsunami in the ocean is 500km h, the tsunami will reach the Maldives beach after 1500km divided by 500km h equals 3h, and the children should immediately run to the highland 3000m from the coast, and the speed of the children fleeing to the highland is 100m min, so the time for the children to run to the highland is 3000m divided by 100m min is equal to 30min, 3h-30min=, Therefore, you can only survive by receiving the warning one hour after the tsunami warning occurs, that is, at 11 o'clock.

There is a circuit diagram analysis that two resistors are connected in parallel, A1 measures the total current, A2 measures the current of R2, and the voltmeter measures the power supply voltage.

The resistor R1 is marked with "6 La", and its maximum voltage is 6VR2 is marked with "3 1 2A", and its maximum voltage is two in parallel, and the voltage is equal, so it can only be taken, otherwise R2 will be burned out.

In this way, i1 = u r1 = i2 = i = i1 + i2 = the allowable power supply voltage is The current through the ammeter A1 must not be exceeded.

The mains voltage and current through ammeter A1 must not be exceeded.

The two resistors are connected in parallel, the actual voltage is equal, and the minimum rated voltage must be met to protect the resistor, and the ammeter measures the total current.

Hello! The calorific value per unit time of the electric blanket is the original value or half of the original value, that is, the power becomes half of the original.

First of all, if the parallel resistor is the same, the voltage of the electric blanket will not change, and the power of the electric blanket will not change because the parallel voltage is the same, so it is in series.

From p=u 2 r, we can know that the voltage becomes a multiple of the original, that is, 110 2v, then the series resistance voltage is u=(220-110 2)v, and the current of the series resistance is equal to the current of the electric blanket i=110 2 r1, so the series resistance is r=u, i=(220-110 2) (110 2 r1 )=( 2-1)r1, I hope to adopt.

Suppose the connected resistance is r, the resistance wire resistance is r1, and the power supply voltage u=220v;

When the heat per unit time of the electric blanket is half of the original, the two resistors are connected in series;

The power consumed by the resistance wire is: p 2 = u1 2 r1 original power p = u 2 r1;

Substituting the formula, so after the power is reduced, the voltage at both ends of the resistance wire is u1 = ( 2 2)u, and the circuit current is i= u1 r1=( 2 2)u r1;

The magnitude of the resistor r is r=(u-u1) i=( 2-1)r1

When the switch is closed, R2 is short-circuited and does not work, which is the original power, and when the switch is disconnected, R1 R2 is connected in series, and the power is half of the original.