In the second year of junior high school, the physics questions will be solved, and the correct rate

26.This is due to the exothermic reason of liquefaction, spraying oranges with water, and if the temperature is too low at night, the water will liquefy and release heat, preventing frostbite from oranges, which is the same effect as putting a bucket of water in the cellar to prevent the cellar temperature from getting too low.

27.(1) The temperature of the things taken out of the refrigerator is very low, and the water vapor in the surrounding air liquefies into small water droplets when it encounters cold objects, and attaches to the object to form "sweaty" water droplets.

2) The refrigerator is characterized by low temperature, sealed, no light, and the content of water vapor in it is relatively small, and most of it turns into ice, so it is a good place to prevent moisture, but the premise is that it is tightly packed. It should not be opened immediately after taking it out of the refrigerator, because the temperature of the tea bag taken out of the refrigerator is very low, and if it is opened, the water vapor in the air will liquefy into small water droplets that adhere to the tea leaves, causing the tea to be damp.

Because the temperature of the tea leaves is lower than room temperature after refrigeration, once the tea leaves are taken from the refrigerator to room temperature, the hot water molecules in the indoor air are liquefied by cold. So water droplets appear on the surface.

You can't open it right away, because the tea leaves are afraid of moisture, and if you open it right away, hot air will enter, which will also lead to liquefaction.

27.(1) The temperature of the tea leaves taken out of the refrigerator is low, and the air around the tea leaves liquefies when cold to form "sweat";

2) No, the tea leaves need to be stored in dry conditions; If the tea package is opened immediately, the tea leaves in the bag are easy to "sweat", which is not conducive to storage; It is better to open the package when the temperature rises to room temperature.

p = ui = u 2 r with human data Bu Naide r = 36 2 400 = 324 100 = 81 25, buried Xun when the power of the heating element is 300W, the voltage U1, the type liquid spring then U1 2 r = 300 to obtain U1 = 9 2 3V. Let the resistance value of the external resistor be r1, then r r1 = u1 (u-u1) with the value of the person data r1 [calculator is used].

What do you want to prove, just a picture?

I did the math, and it turned out that the answer in the book was also wrong?

First of all, according to the case of 400W, the resistance of the starting heat body is calculated, and the formula is p=U2 r, then r=U2 p=36*36 400=

Next, calculate the resistance of the external pulse shield in series according to the situation of 300W, and first calculate the current through the heating element at this time

There is p=i 2*r, so i=, and then calculate the external resistance, x=u i-r= and calculate, if the external resistor is put in the box, it is ......The answer is undoubtedly wrong.

36 2 300= 36 2 400= The answer....Ji Tsai is in trouble....Speechless.

1.The picture above is the modified one.

When S1 and S2 are closed, the external power group is short-circuited, which is equivalent to the heating element connected in series at both ends of the power supply, which is 400W.

When S1 is closed and S2 is opened, it is equivalent to the heating element connecting the external resistor in series, which is 300W at this time.

2.First of all, according to the case of 400W, calculate the resistance of the starting heat body, the formula is P=U2 R, then R=U2 P=36*36 400=Ohm Next, according to the situation of 300W, calculate the external disturbance resistance in series, first calculate the current through the heating element at this time has P=I2*R, so I=Amps, and then calculate the external resistance, X=U I-R=Ohm

Of course, there is a possibility, that is, the modification diagram you sent above is different from the square side circle method of the answer, because it can also be connected in parallel with a resistor or something There are n kinds of modification methods

1.What is the work done by a person to overcome gravity?

Every time a person wants to overcome gravity, the work done is w1=mgh=80*10*he jumps 800 times in ten minutes, and the total work done to overcome gravity in ten minutes is w=800w1=800*40=32000j2What is the average power of a person to do work against gravity?

p=w/t=32000/10*60=

3.If the energy consumed by a person to do work against gravity is only provided by fat, how much fat can be burned in theory? (The energy provided per kilogram of fat is, g = 10n kg).

Let the fat consumed be m kg.

The total energy of m kg of fat is:

The total energy consumed by jumping rope is 32000J

These two energies are equal:

m=2*10^-3kg

The work done by gravity w=mgh*n (n is the number of degrees).

w=80*10* j

Power p=w t

p = 32000 (10*60) = 53, 33 w burn fat = w 10 7j = kg

5cm W FS 800N Answer: The work done by a person to overcome gravity is 40J

40J 800 32000J P W T 32000J 600S 53W The average power of the respondent to do work against gravity is 53W

A...

There is no comparison.

The screws are stationary in the horizontal direction relative to the maje, so they just hit his head and gravity provides acceleration Everything else is inertial in the process of two-force balance. The key is that the same object is subjected to a force equal to a large opposite.

5.No picture.

It's so tragic, I often type a lot of words, and the result has been adopted, and it was unsuccessful in the past, and now it is directly submitted to the ......

Analyze and analyze, junior high school physics is popular science, as long as you have a general concept of physics.

is a unit of mass and 49n is a unit of force, and the two cannot be compared, which is obvious, just as it is a truth that length and mass cannot be compared.

Note: In fact, there has been a unit system in history that uses "kg" to express the magnitude of the force, which is generally read as "kilogram force", for example, 1 kilogram force represents the gravitational force of 1kg of an object. But this question is obviously not a test ......）

c。Ma Jie's question. This is a little more difficult, and junior high school may not be too easy to think of.

When the nail falls, it goes forward with a constant speed and goes with the boat, and it will not be because the speed of the fall is gone, and Ma Jie also walks with the boat, so they both move forward at the same speed. At this time, the nail also has a falling speed attached, which is equivalent to falling straight on the head.

d。Olympic one. I am more disgusted by this question, and I think it is not good, because inertia is everywhere, and the four options are related.

I think it would be clear to change the title to "What can be done with the following movements even if the object has no inertia". A jumps up and gets off the ground, and if there is no inertia, it will not continue to rise, and it will come down directly under the action of gravity. b If there is no inertia, the shot put will not go forward if it is not forced, and it will fall.

c If there is no inertia, the bullet will fall without the forward force. dIf there is no inertia, the athlete will still fall ...... if he is constantly under gravity

d。Soccer problem, this question clarifies the concept of the balance of forces. The balance of two forces is actually the meaning of "two forces act to balance an object", so it is the object that is balanced, and it is necessary that the two forces must act on an object first.

So did you find that a force is a force on the ball is a force on the grass, and c is also this error. b Obvious friction is on the ground, gravity perpendicular to the ground, cannot be in the same straight line, not a balancing force.

Straw problems. There is no picture.,It's best for the landlord to make up the picture.。 But I guess it should be using a syringe to inject gas into the bottle, and the air pressure obviously rises, "greater" than the air pressure in the glass tube, and the phenomenon is that the liquid level in the straw rises.

This obviously can't be verified to be pressed up, because the effect of sucking up is the same, you just press it up and you can't draw the conclusion that "it can't be sucked up". It's like you can smash a walnut open with a hammer, you can squeeze it open with a door, and now do an experiment and smash a walnut open with a hammer, and then you can conclude that "the door can't squeeze the walnut open" is wrong.

Question 1: Units cannot be compared.

Question 2 Since it is a constant velocity, that is, the relative velocity is 0 Hit the head 3 Question d The first few are all moving in the direction of the initial velocity, and the athlete in the d option is jumping upwards and the inertia is upward.

Question 4 Definition of equilibrium force: A force acting on the same object of equal magnitude and in opposite directions. So choose D

Question 5 Less than There are bubbles in the water Can't (I'm not sure, I don't know what conditions are observed).

Gravitational acceleration cannot be determined, so it cannot be compared)

The nail is also made of uniform linear motion)

Diving is the use of gravity).

The object under force is the same and in a straight line).

Hello! 1.A solid metal ball weighing g, hung under a spring and immersed in some kind of liquid, when 2 3 of the volume of the metal ball is immersed in the liquid and at rest, the spring dynamometer reads f, then the ratio of the density of the metal ball to the density of this liquid is:

To the process, explain).

2.The metal block is tied with a wire and placed in a cylindrical container with a bottom area of 500 square centimeters and a certain liquid, and the depth of the liquid in the container rises from 20 cm to 21 cm

1) the buoyancy experienced by the metal block in the liquid;

2) the gravitational force experienced by the metal block;

3) The density of the metal. (g takes 10n kg) [again, to the process, explain]3An iron ball with a volume of 1 cubic decimeter, hung on the hook of a spring dynamometer, and then submerged in water, the spring dynamometer indicates that the weight of the ball is 4 5

g = 10n kg, p iron = cubic meters).Seeking:

1) the buoyancy of the iron ball;

2) the gravitational force experienced by the iron ball;

3) Is this iron ball solid or hollow? If it is hollow, what is the volume of the hollow part?

By Q = cm T, the current provides 10g * 50 * joules, the actual power is 2100000 (35 * 60) = 1000W, the original water heater resistance is 220 * 220 ohms, by P=U*U R, the water heater voltage is 176V, the loss of 44V on the wire, the wire resistance is Europe, now the two water heaters are connected in parallel, the resistance is Europe, the voltage is 220V, the voltage is Xv, 220 X=, X=330V

Water is v1 m1 and sand is v2 m2 units l kmv1+v2=10

1v+ two-type collapse shouting Yunlian infiltration bridge solution v2=

m2=p2xv2=group beam.

36V constant power supply, 36V constant power supply, the actual power of the heating element of the leather socks is 400W, R heat = 220 400

The voltage in front is 36V, and the formula behind the grip is 220V, and there is a problem here.