Mathematics and Physics in the second year of junior high school, asking, urgent, high reward

Question 1: Yes, due to the distance between the Sun and the Earth, sunlight can be considered as parallel light, and all three angles of a right triangle are equal, and ASA can prove congruence.

Question 2: Spread out as much as possible, maximize the light receiving area, pay attention to ventilation, speed up the evaporation rate, and turn over the sun more.

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The diagram is wrong because the sun is far away from us, so the sunlight is approximately parallel light, so it is correct. There are many conditions, and there is also an angle that is the angle between the sunlight and the ground, so that the equal conditions are enough.

2.Spread the wheat (to increase the surface area of the liquid).

Place in a sunny and ventilated place (increase the temperature, reduce the humidity, and increase the surface area above the liquid).

1. Correct. 2. Air humidity, wind speed, light, and drying area.

1) See figure. In this case, the height of the two rods is different.

2) The wheat should be spread evenly, the heating area should be increased, and the overall water evaporation area should be increased.

2。When the two desks are next to each other, the sound is loud.

Sound travels by solids.

When there is a small slit between the two desks, the sound is quiet.

Sound is transmitted by solids and gases.

3。Yes, you can hear the sound of the shore when you dive into the water while swimming.

4, it seems that the solid "liquid" gas, this one goes to the textbook by himself.

The first sound that came through the stick.

6.Put 1000

7。There are experiments in the textbooks.

8。Oxygen is needed for the combustion of matter, and there is no oxygen under vacuum conditions, so things cannot be burned, and in the same way, the propagation of sound requires a medium, and it is impossible to transmit sound in a vacuum state.

Not equal to 2; x is less than 1 7

10。The numbers below the root number are all greater than or equal to 0, the opposite number of positive numbers is negative, and 0 is itself.

So there is x-y=2, x+y=1

x= y=

So 3x-2y=

If I don't learn physics concepts well, let's talk about mathematics

1) 3x+2 should be 3x+2 greater than or equal to zero in the root number, so x -2 3x-2 should not be equal to zero, so the answer is x -2 3 and x ≠22) is similar to the above idea, 4x+3 is greater than or equal to zero, so x -3 41-7x because he is the denominator can not be equal to 0 but can only be greater than 0, so x 1 7 The answer is 1 7 x -3 4

2. If it is the opposite number, x-y+2 and x+y-1 can only be equal to zero, so solving the system of equations can give y=3 2, x=-1 2

Therefore, 3x-2y=-3 2-6 2=-9 2 may have errors in your own calculation, for reference only.

1: Air. 2: Desks Desks, air.

3: Yes, the fish is in the water, and the person walks close to the fish.

4: The fastest solid gas is the slowest in the middle of the liquid.

5: 2 times iron.

1.Workpiece and grinding wheel.

2.(1) Large wood (table).

2) Small wood (table) and air.

3.Yes, water ballerinas can hear ** sound underwater.

4.Solids are greater than liquids and gases.

5.Twice iron pipes.

Approx. seconds. 7.See the textbook for the table experiment, or rope** (two paper tubes, one thread in the middle).

8.The five mediums of the universe are silent. Even if there is a medium, you should see the fire first, followed by a loud noise. There is no oxygen in the vacuum and cannot be burned.

1.The problem is not clear, is it 3 under the root number or 3x+2 under the root number, the same question later!

2.questions to use.

Physics 2(1) No.

2) When the two desks are next to each other, the volume of the sound: loud.

What does sound travel by: solid (table).

When there is a small slit between the two desks, the sound is small.

What does sound travel by: gas, solid (air, table).

3. Yes, the fish in the water heard the footsteps on land and were scared away.

4. Solid sound transmission effect is the best, followed by liquid, and gas is the worst.

5. Twice, iron pipe.

Second. 7. The question on the table in front.

8. One is that the speed of light is faster than the speed of sound, and the other is that the universe is a vacuum and cannot transmit sound.

m s set the velocity to v

25 6 * 144 = 200 + 144 * v v = 25 9 * is equivalent to a multiplier sign.

4.No. 5.Greater than (some forgot).

6.As long as the quality is compared with the price-quality ratio. mWinter=,mSummer=,51 12=, 25 6< so Summer is higher than winter**.

Summer price: 25 6 * 12 = 50yuan According to the quality, take 25 6 or yuan kilograms.

1: Xiao Ming's actual passing distance: s=vt=15km h then Xiao Gang traveled the same distance during this period =

Small rigid velocity = 2: choose b

3. In the middle, it should be put from large to small in quality. So ......I don't need to say it.4 The objective lens becomes a real image, and the eyepiece becomes a virtual image.

5 choose A6 Winter quality per bottle: M winter = winter v per kilogram** = 55 non-stop).

Mass of each bottle in summer: m summer = summer v

** per kilogram ** = 51 12 so high in summer**).

If ** is the same. Then the summer price = yuan.

The medium gas ** is yuan kilograms.

One, stress.

1.Concept: Objects are perpendicular to each other due to their mutual extrusion.

2.Vertical. II: 1The magnitude of the pressure and the area of the force.

2.Sponges, weights, small tables.

3.Force area, pressure.

**Dian question 1: D, drawing, try it yourself.

Question 2: B Variant Training 2-1: BCD

Variant Training 2-2: The degree of depression of the sponge.

In winter, there is a large temperature difference between indoor and outdoor, and the temperature in the house is high, and the water vapor in the air becomes hot, and when they are fluttering, they condense when they touch the cold glass.

The direction of the pressure is perpendicular to the contact surface and directed towards the pressed object.

28 The following substances exist: glass, copper, mercury, peanut oil, graphite Please divide the substances into two categories according to their physical properties and state the basis for your classification. It can be classified according to the different (shapes of objects).

One category is: glass, copper, graphite; Features: (solid); The other category is:

Mercury, peanut oil, Features: (liquid). It can also be classified according to different (conductivity):

One category is: copper, mercury, graphite; Features: (Electrically conductive,) The other category is:

Glass, peanut oil, features: (non-conductive). Classification according to (whether it is metal or not):

One category is: copper, mercury, characteristics: (metal); The other category is:

Glass, peanut oil, graphite, features: (non-metallic).

30 In winter, when you touch a metal object with your hands, you feel very cold, but when you touch wood, you don't feel particularly cold, because metal (conducts heat) more than wood.

31 When Edison invented the electric lamp, he chose tungsten filament because of its high melting point, and the filament made of tungsten filament is not easy to burn.

Have you been playing for a summer vacation, didn't finish your physics homework, and now you're blind?

What's the problem?

A The power of the soldering iron becomes 1/4 of the original, and it can be seen from the p u r that the voltage of the soldering iron should be changed to 1/2 of the original, so the resistance of the selected bulb should be the same as the resistance of the soldering iron, and the specification should be "220V 100W".

B When S is dialed to 1, the lamp does not work, and the soldering iron gets the full voltage of 220V, which is just the rated voltage of the soldering iron, so the soldering iron is in working condition.

c When S is dialed to 2, the lamp is connected in series with the soldering iron, and the voltage of the soldering iron is less than 220V, which is in an inactive state.

D The total power of the whole circuit in the non-working state of the electric soldering iron is: 25W+25W 50W Under normal working conditions, the total power of the whole circuit is: 100W, compared with the electric energy that can be saved: 100W*1S-50W*1S=50J

Look at the diagram is not clear, choose one of b and c (I don't know b, c you analyze it yourself), a and the soldering iron with the same power (same resistance), d power saving 50w reverse calculation = 50j. Hope it helps. Thank you!

There are no pictures, why can't you guess the analysis???

1. Scale, beaker, water.

2. Use a scale to measure the thickness of the K letter to δ, add water to a beaker, measure the volume of the K letter (know how to measure it) v, calculate the area of the K letter as v δ, then the cost of gold foil = v δ gold price.

The density of pure gold is:

100²-99²+98²-97²+·2²-1²=（100+99)(100-99)+(98+97)(98-97)+·2+1)(2-1)=1+2+3+··100=5050

The ice-water mixture is 0 degrees Boiling water is 100 degrees, and the temperature difference of 100 is actually 105 degrees Celsius, so the scale of the thermometer is inflated, so 15-(-2)=17 17 (1+

I pick 1 and 2

Math: 100 squared minus 99 squared plus 98 squared minus 97 squared......Add 2 squared minus 1 squared = (100 + 99) (100-99) + (98 + 97) (98-97) ...2+1)(2-1)

100+99+98+97+..2+1=5050 Physics: [47-(-2)]: Actual temperature = [96-(-2)]: 100 Solution Actual temperature = 50

The difference between ice and hot water is actually 100 degrees, and now the difference is 105 and the answer is 15*

Mathematics: original formula = (100 + 99) (100-99) + (98 + 97) (98-97) + (96 + 95) (96-95) +2+1)(2-1)

Physics: Let the actual temperature be t, and the thermometer is displayed as t1, a, b is the proportionality constant t1=at+b

When t=0, t1=-2.

b = -2 when t = 100 and t1 = 103.

103=100a-2

a=when t1=15.

t = i.e. the actual temperature is in degrees.