There is a junior high school physics competition question that I would like to ask all the masters

The more down the time.

The more the density meter is submerged in the liquid.

The more buoyancy he suffers, the greater the buoyancy.

That is, the less dense.

That's it.

The further downward, the greater the water pressure created by gravity.

Did you make a mistake? Is it that the 'spacing' of the carved lines on the third floor is getting smaller and smaller?

p represents the density v1 density of the density meter, the volume of v2 discharges the liquid, the density of the p1 density meter, and the density of the liquid to be measured p2.

p1v1g=p2v2g

p2=p1v1/v2

P1 V1 is a fixed value P2 is inversely proportional to V2 From top to bottom, the scale value of the density meter gradually decreases, so the spacing of the scale marks of the density meter is uneven, and the spacing of the adjacent graduation lines is smaller as the downward.

This question has been solved incorrectly from the step down, but it has a correct answer, which is really strange Hehe...

10 RL - Square + 90 RX

i.e.: rl - square + 9 rx

Then we need to find the maximum value of the equation on the right:

When rx = -b 2a = 50, the maximum value is 225

So rl 225

That is, the minimum value of RL is 225

One thing to note in this problem is that the range of rx is 0 100, and then we can find the maximum value of the equation on the right).

After thinking about it for a long time, I forgot all the previous knowledge, I haven't solved this kind of problem for a long time, and my brain is not as flexible as before.

The person who came up with the problem didn't pass the math, and the inequality solution turned out like this.

This question is misprinted, the answer is correct, and the penultimate step is correct.

I only found similar titles.

Plant transpiration absorbs the heat from the canopy, so the temperature in the shade is lower than in the surrounding area, and people go from sunshine to no sunshine is the presence or absence of heat source, and this process naturally makes people's body surface temperature drop and feel much cooler.

Plant respiration is the process of converting organic matter into inorganic matter, releasing carbon dioxide and water, and it's actually a complex chemical reaction that is exothermic, but the amount of heat released is very small and it doesn't have any effect.

Whether it's in the sun or in the shade of a tree, we're all sweating, and that's the main way we dissipate heat, but it has nothing to do with the title, and the main meaning of the design is: the reason why it's hot in the sun and cool in the shade, not how people get rid of heat.

The sun increases the energy on the surface of the human body through radiation, which increases the temperature and makes people feel hot, which is why "people are unbearably hot in the middle of summer, under the scorching sun."

Solution: This question can be divided into two parts of movement, this question mainly tests the relative movement 1, the correspondent and the team move forward together.

2. The correspondent and the team walk in the opposite direction.

First of all, V team T1 - V team T1 = L team (the correspondent and team take the same time, L is the relative displacement of the two).

Secondly, V people T2 + V team T2 = L team (same as above) V team (T1 + T2) = S team So, S people = 2L team = 240 meters.

The upstairs must be wrong, the team walked 288 meters slower than him, and he only walked 240??

The correct solution is 432 meters.

Same upstairs.

V T1 - V Team T1 = 120

V T2 + V T2 = 120

Team V (T1+T2) = 288

There are four unknowns in the previous equation, but we can solve it using the elimination method: v man = team and then substitute v team (t1 + t2) = 288

528 meters.

S1: The team is 120 meters long.

S2: The team travels 288 meters.

Because the Communicator's speed is greater than the team's forward speed and the distance the team travels is greater than twice the length of the team, the Communicator will not repeat the distance traveled at the front of the team. The total distance is the length of the team, and the round trip is 240 meters, plus the distance traveled by the team is 288 meters.

Total length s=s1+s1+s2

This problem is not easy to do, it is better to use the following solution.

o---o___o120m 168m 120m

a m |As shown in the figure above, the team originally walked forward 288 meters to the ** section after the --section, the segment indicates the position where the communicator arrived at the head of the team, and the ** section and the intersection of the place are a meter long.

Since the speed is the same, the ratio of the distance traveled at the same time is the same, and there are two periods of the same time in the figure, when the tail of the team walks to the place and when the team walks to the @ place, they arrive with the same communicator. is equal to the second arrival @.

From the above, the following conclusions can be drawn:

168+a/288+a=120-a/a

Solution: a=72m

The total distance is 288 + 72 x 2 = 432m

(1) The transformation of energy in the above-mentioned device is from chemical energy to electrical energy. After a period of time in this experiment, the change in pH of the solution is increased (increased, decreased, unchanged), and the electrode with a decrease in mass is Zn.

2) If only magnesium flakes and carbon rods are used as electrodes, and other experimental conditions remain unchanged, according to the experimental data in the above table, you guess that the voltage generated should be greater than the voltage generated by the three batteries in the table (optionally "all large", "all small", "between them" or "injurable").

3) connect three single fruit batteries with carbon rods and zinc sheets as electrodes in series, connect a small bulb with the nameplate of "2 5v 0 3a" in series to this circuit, after the switch is closed, the small bulb does not shine normally, the reason is that the internal resistance of the power supply is too large. 。

(1) The transformation of energy in the above device is from chemical energy to electrical energy. After a period of time, the change of pH of the solution is increased (increased, decreased, unchanged), and the electrodes with reduced mass are Zn, Fe.

2) If only magnesium flakes and carbon rods are used as electrodes, and other experimental conditions remain unchanged, according to the experimental data in the above table, you can guess that the voltage generated should be greater than the voltage generated by the three batteries in the table (optionally "all large", "all small", "between them" or "injurable").

3) connect three single fruit batteries with carbon rods and zinc sheets as electrodes in series, connect a small bulb with the nameplate of "2 5v 0 3a" in series to the circuit, after the switch is closed, the small bulb does not shine normally, the reason is that the internal resistance of the power supply is too large, and the voltage obtained by the bulb is too small.

Please be sure to explain the reason in detail, thank you!

1。Chemical.

Enlarge. Zinc flakes (none of them are carbon rods).

2。All large. 3。The current is too small.

It should be right! Please advise me if it's not right!

When the voltmeter is connected to B, the obtained voltage is the real voltage at both ends of AB, that is, UAB = 12V, and the voltage at both ends of the resistance is obtained when the voltmeter is connected to A, so that the voltage at both ends of the ammeter is 12V-10V=2V, then the internal resistance of the ammeter is 10 ohms, so that the voltage division on the ammeter when the voltmeter is connected to B is again, the voltage on the resistance is at this time, and the resistance magnitude is ohm, and the solution is obtained.

In fact, what we are looking at is just the external and internal methods of a high school.

Such as upstairs

I didn't go to high school, but I still know a lot about circuits, and the ideas analyzed upstairs are very clear, just look at him, I won't say more.