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Questioner: Suzuki Ye Xue-Magician Level 4.

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Answer will get 2 points, if the answer is accepted, you will get bonus points and 20 points.

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References:

Anonymous answer integral rule

Answer *** 1

The 14th National Junior High School Applied Physics Competition contains answers.

Matters needing attention

Fill in the area, school, name and test number first.

Write with a blue or black pen or ballpoint pen.

There are seven major problems in this paper.

Answer time: March 28th, 2004 (Sunday) at 9: 30am ~11:10.

The total score of the topic is one two three four five six seven.

mark

chessman

1. Only one of the following questions is correct. Fill in the letter before the correct answer in the square brackets after the question (*** 12 points, 3 points for each small question).

1. The TV can be turned on and off with the remote control. The remote control is used to control the TV set.

A. red light B. infrared light

C. violet light D. ultraviolet light

2. When cooking, if you accidentally splash water droplets into the hot oil pan, you will hear a beep and the oil will splash out. The main reasons for this phenomenon are

A. water is a poor conductor of heat. B. the temperature of water droplets is different from that of oil.

C the boiling point of water is lower than the temperature of hot oil. D. the specific heat capacity of water is higher than that of oil.

In the children's playground, the photographer took pictures of cartoon characters. When focusing, he found the position of cartoon characters on the ground glass as shown in figure1a. In order to position the cartoon characters on the ground glass as shown in figure 1B, the photographer should correctly position the lens.

A. move to the lower left

B. Move to the lower right

C. Move to the upper left

D. Move to the upper right

4. Figure 2 shows four control circuits of stair lighting designed by Xiaoming, in which S 1 and S2 are upstairs and downstairs switches (both are single pole double throw switches). You need to toggle any switch to change the original lighting or extinguishing state of the light. In practical application, the best scheme is

Two. Fill in the blanks (***20 points)

1.(4 points) At the bottom of the aluminum pot used for boiling water, there are often several uneven concentric circles, whose main functions are:

( 1)_______________________________________;

(2)_______________________________________。

2.(3 points) Xiaofeng's height is 1.70cm, his eyes are 8cm above his head, and he stands upright on the horizontal ground and looks at the mirror. If he wants to see his feet from the plane mirror hanging vertically on the wall, the height of the bottom of the mirror from the ground should not exceed _ _ _ _ _ meters.

3.(4 points) In the spring of 2003, SARS epidemic occurred in some cities in China, and sprayers were widely used for disinfection in public places. Figure 3 shows a schematic diagram of a sprayer, and the physical knowledge required for its working principle is as follows (only two items are written).

( 1)_______________________________________________;

(2)_______________________________________________。

4.(5 points) On June 65438+1October 65438+June 6: 54, 2003, Shenzhou 5 spacecraft successfully completed the first manned space flight in China, and the return capsule landed safely at the main landing site in Inner Mongolia.

(1) The energy conversion during rocket launch is mainly _ _ _ _ _ _ _ energy into _ _ _ _ _ energy.

(2) When the spacecraft flies around the earth after turning off the engine, if the following experiments are carried out in the cabin, the most difficult thing is _ _ _ _ (fill in the blank): a. Measure the temperature with a thermometer; B, observing the onion skin with a microscope;

C, filtering with a funnel and filter paper to remove the sediment in the water.

(3) If crop seeds are carried into space and then brought back for planting experiments. Its purpose is to

__________________________________________________________。

5.(4 points) Electric hotbed is one of the hotbeds commonly used in early spring seedling raising in northern China. The manufacturing method of the electrothermal hotbed is: firstly, dig the bed soil about 20 cm thick, lay a layer of wheat straw or sawdust under the bed, and then lay a layer of plastic film. Spread the heating wires evenly on the plastic film with the spacing of 10cm, and then put the bed soil back, so that the electric hotbed is ready.

The thermostat of the electric hotbed is equivalent to a variable resistor, and its resistance changes with the temperature. It can automatically control the current through the heating wire according to the temperature, so as to realize the automatic control of the hotbed temperature. When using, please connect the thermostat with the electric hotline. The electric hotline shall not be knotted, crossed or overlapped, otherwise it may be dangerous due to _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _. This method is to use _ _ _ _ _ _ _ _ to obtain the suitable temperature for seedling growth.

III. Briefly answer the following questions (***20 points)

1, (4 points) The design scheme of a railway station in a city is shown in Figure 4, and the entrance and exit tracks and platforms form a gentle slope. What are the advantages of this design from the perspective of energy utilization?

2.(4 points) On the side of ocean-going ships, several "load lines" are drawn. When the ship is fully loaded, the water surface cannot exceed the specified load line. As shown in Figure 5, it is a schematic diagram of ocean-going ships and their load lines, where W is the North Atlantic load line and S is the Indian Ocean load line. Use the physical knowledge you have learned to analyze what this logo shows.

3.(6 points) The front windshield of cars has a certain inclination angle, while the front windshield of large vehicles such as trucks and buses is almost vertical. Please use optical knowledge to analyze the reason why the front windshield of the car is installed like this (you can draw a picture to explain).

4.(6 points) In production and life, due to friction and other reasons, static electricity is often generated, which can be used and harmful.

(1) Please illustrate the advantages and disadvantages of static electricity in people's life and production.

(2) Please give examples to illustrate the specific measures to prevent the adverse effects of static electricity.

4.(8 points) Xiaoming designed a water tank that can automatically flush the toilet in the public toilet. This kind of water tank can automatically open the drain valve after storing a certain amount of water at a small flow rate continuously supplied by the tap water pipe, so that a large amount of water can be used to flush the dirt in the urinal. Fig. 6 is a schematic structural diagram of this water tank. It is known that the bottom of the water tank is square, the side length l=40cm, A is a circular drain valve, and the diameter d 1=8cm. Its mass and thickness can be ignored, and the float B can just connect the drain and the connecting rod, and the length of the connecting rod is h0= 10cm. Float B is a hollow cylinder with an outer diameter d2=8cm, a height H = 30 cm and a mass m=0.4kg. It is assumed that the water in the water tank can be drained clean every time. The calculation shows: (1) How high is the water tank so that the water will not overflow from the upper part of the water tank? (2) If the flow rate of the tap water pipe is 0.2m3/h, how many minutes is the time interval from the end of one discharge to the next discharge?

5.( 12) The school will hold a sports meeting, and several students will discuss how to throw the shot put further. Chen Ping said, "The higher the throwing point, the farther it will be thrown." . Wang Li said, "The faster you throw, the farther you throw." . Li Ming said, "Let's explore through experiments."

After discussion, we put forward the following conjecture.

Guess 1: The distance of shot put may be related to the height of the shot put point.

Conjecture 2: The distance of shot put may be related to the speed of shot put.

Guess 3: The distance of shot put may be related to the angle of shot put (the angle between throwing direction and horizontal direction).

In order to test whether the above conjecture is correct, they made a small ball catapult, as shown in Figure 7. It can make the ball shoot at different speeds and directions, and the elevation angle of the shooting direction to the horizontal direction can be read by a protractor fixed on the iron frame. They obtained the experimental data in the following table through seven experiments ("shooting distance" refers to the horizontal distance).

Experimental serial number, ejection point height

H/m injection speed

V/(m s- 1) exit elevation angle

Shooting distance

l/m

1 0.5 5 30 2.9

2 0.5 10 30 9.6

3 0.5 10 45 10.7

4 1.0 10 45 1 1. 1

5 1.5 10 45 1 1.5

6 0.5 10 60 9. 1

7 0.5 15 30 20.7

Please answer the following questions according to the information and relevant evidence collected above.

(1) In order to verify the conjecture 1, the experimental data with serial number _ _ _ _ _ _ _ _ _ _ _ _

Because _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.

(2) In order to verify conjecture 2, the experimental data with serial number of _ _ _ _ _ _ _ _ _ _ _ _ _

Because _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.

(3) In order to verify conjecture 3, the experimental data with serial number _ _ _ _ _ _ _ _ _ _ _

Because _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.

(4) Through the above experiments, how do you think we can put the shot put further?

6.( 12 minutes) Figure 8 is a schematic circuit diagram of a motorcycle turn signal. Among them, "RJ switch" is a switch controlled by relay, which can make the circuit on and off intermittently, and D is the indicator light. When S is set at the position of 1, the two right turn signals in front of RD 1 and RD2 are on, and the right turn signals are sent to the outside, and the D light flashes at the same time, indicating to the driver that the turn signals are working normally. Turning left is the same as turning right. If all four turn signals use "6V, 10W" bulbs and d uses "6V, 1.5W" bulbs, the voltage across the power supply is 6V. Try to explain by calculation why if S is set at any position of 1 and 2, the D light will be on, but the left and right turn signals will not be on at the same time.

Vii. (16) The following table lists the parameters of domestic gas water heaters produced by a factory. The "rated heat load" in the table refers to the heat generated by fuel combustion within 1h at full load.

Product name gas quick water heater

Product model JSY5-C JSR5-C JST5-C

Suitable for gas, liquefied petroleum gas, artificial gas and natural gas.

The rated gas pressure is 2800-3000 Pa.

280-300mm water column 800-1000pa

80- 100 mm water column 2000-2500 Pa

200-250 mm water column

The rated heat load is 37mj/h.

The rated gas consumption is 0.368×102m3/h1.964×102m3/h1.04×102m3/h.

Thermal efficiency > 80%

The applicable water pressure is 0.04-1.0 MPa (0.4-10 kgf/cm2).

The temperature of hot water output is increased by 25℃ per minute.

Temperature rise 40℃ 3l/min.

Temperature rise at 55℃ is 2l/min.

Interface size gas inlet G 1/2 "

Cold water inlet G 1/2 "

Hot water inlet G 1/2 "

Overall dimensions are 406 mm (height) ×293 mm (width) ×230 mm (thickness).

Weight 6.2 kg

(1) Calculate the heat generated by the combustion of 1m3 liquefied petroleum gas, artificial gas and natural gas respectively.

(2) According to the values in the table and your existing knowledge, discuss the meaning of "mmH2O" in the line of "rated gas pressure".

(3) Wang Baocheng said that the number "1" in the column of "hot fish yield" seems to be behind 5, 3 and 2, but something seems to be missing before "/min". Please judge the correct values and units of the three parameters in this column by calculation.

(4) The column of "thermal efficiency" is the reference value, and the column of "hot water output" is the measured value of the sample by the manufacturer. Calculate the thermal efficiency when the temperature rises to 25℃ and 55℃ respectively, and explain the reasons for the different thermal efficiency in these two cases.

The 14th National Junior High School Physics Application Knowledge Competition

Reference solution and grading standard

1. Answer and grading standard *** 12, 3 points for each small question.

1.B 2。 C 3。 B 4。 A

Two. Reference answer and grading standard ***20 points

1.( 1) increases the heating area, and (2) enhances the mechanical strength. Deduct 2 points for each vacancy.

2.0.8 1, 3 points.

3. Using lever to change the magnitude or direction of force, the gas volume decreases and the pressure increases. Deduct 2 points for each vacancy.

4.( 1) chemistry, machinery (or kinetic energy and potential energy), 1. Answer an empty question correctly without deduction.

(2)C, 2 points.

(3) See if the gene of the seed has changed under weightlessness, 2 points.

5. The series electric heating is too concentrated, and the local temperature is too high, which burns out the insulation layer of the electric hot wire, leading to short circuit or leakage, and the thermal effect of the current. The first space is 1, the second space is 2, and the third space is 1. Different expressions, the same meaning, the same score.

Three. Reference solution and grading standard ***20 points.

1. Part of the kinetic energy of the car when it enters the station is converted into gravitational potential energy to reduce the mechanical energy lost due to braking (2 points); When the car leaves the station, the stored gravitational potential energy is converted into kinetic energy, which plays an energy-saving role. (2 points)

4 points for the whole question, and 1 point for failing to answer the energy-saving function.

2. The seawater density in different sea areas is different, and the seawater density in the North Atlantic is higher than that in the Indian Ocean. 4 points for the whole question.

3. In order to ensure the safety of driving at night. The front windshield of a car is installed obliquely because

The light from the vehicle behind hits the front windshield and reflects obliquely downward; When the scene inside the car is illuminated, the image formed by the front windshield is located diagonally above the driver. In this way, the driver in the car will not be disturbed by the reflected light.

Whether using words or drawing, give 3 points for basic correctness and 3 points for clear expression, only because of the reflection law of light, give 1 point.

4.( 1) Examples of using static electricity, for example, people can use static electricity to remove dust and copy. Give it two o'clock. Examples of electrostatic hazards, such as wearing chemical fiber clothes, are easy to "electrocute" or "vacuum". Give it two o'clock.

(2) Specific measures to prevent the adverse effects of static electricity, such as dragging a chain at the tail of a car transporting gasoline to connect with the earth to prevent the accumulated electrostatic discharge from causing a fire. Give it two o'clock.

IV. Reference Scheme and Scoring Standard (8 points)

(1) When the water level of the water tank is H, the pulling force of the connecting rod on the valve A is T, and the valve can just be opened.

For float B, according to the equilibrium condition: mg+t = f float (1 min).

Where f float =? G (h-h0) ( 1)

According to the balance condition of the lever, the drain valve A is: Td 1=? Growth hormone (2 points)

Simultaneous solution:

H = h0，rg-rg) ≈ 0.36m ( 1)

Therefore, the height of the water tank is at least 0.36m.

(2) The volume of a tank of water is: V tank = L2h = (0.4m) 2× 0.36m = 0.058m3 (1min).

Water pipe flow q = 0.2m3/h, the time required to fill a box of water.

T = = = 17.4 minutes (2 points)

Therefore, the time interval for draining the water tank is about 17.4 minutes.

Verb (abbreviation of verb) Reference solution and grading standard (12 points)

(1)3, 4, 5, study the relationship with the height of ejection point, and keep the ejection speed and elevation angle unchanged.

(2) 1, 2, 7, study the relationship with ejection speed, and keep the height of ejection point and ejection elevation angle unchanged.

(3)2, 3 and 6, study the relationship with elevation angle, and keep the height of exit point and exit speed unchanged.

(4) The height and speed of the throwing point should be improved as much as possible, and the appropriate throwing elevation angle should be selected.

Full score 12. (1), (2) and (3) Score ***2 points before each small question, and no points will be deducted if there are mistakes; The fourth space 1 point. Item (4) 3 points.

Reference solution and grading standard of intransitive verbs (12 points)

Because the specification of the lamp D is "6V, 1.5W", the resistance of the lamp D is

RD=U2/PD=24？ (? Integral)

What are the specifications of the turn signal? V, 10W ",so the resistance of the turn signals is R = U2/P = 3.6?

Total resistance of left (or right) two turn signals and lamp D:

R total = rd+r/2 = 25.8? ( 1)

When the motorcycle turns to the right (or left), switch S is connected to position 1 (or position 2). At this time, the voltage at both ends of the right (or left) turn signal lamps RD 1 and RD2 is 6V, and they emit light normally. (2 points)

And the current through the lamp d:

ID=U/R total =0.23A (1 point)

So the power obtained on the lamp is d: pd' = i2rd =1.3w (1min).

Since PD' is close to the rated power (1.5W) of the lamp D, the lamp D can also emit light at this time. (2 points)

Current passing through each bulb of the left (or right) turn signal at the same time: I = ID/2 = 0. 12A (1 min).

Therefore, the actual power of each left (or right) turn signal lamp is:

P Real = I2r = 0.052w (1 point)

Because the P of the left (or right) turn signal lamp is far less than its rated power 10W, the left (or right) turn signal lamp cannot emit light. (2 points)

Seven. Reference solution and grading standard (16 points)

(1) liquefied petroleum gas

=1.0×106j/m3 (1point)

Artificial gas

= 0.19×106j/m3 (1point)

natural gas

=0.36× 106J/m3 (1 point)

(2) Since this line represents pressure, and in each cell, the unit of the quantity in the upper row is the pressure unit Pa, mmH2O is probably another unit of pressure. H2O is the molecular formula of water, and mm is the unit of millimeter. Considering that the pressure generated by a mercury column with a height of 1mm is sometimes used as the unit of pressure, will mmH2O be the pressure generated by a water column with a height of 1mm? You can have a try.

The pressure generated by 1 mm water column is

p=？ GH =/kloc-0 /×103x10x1×10-3pa =10pa (1min).

However, in the row of "Rated Gas Pressure", the value of the quantity in mmH2O is indeed different from that in Pa by 10 times. So mmH2O is the unit of pressure, which is equal to the pressure generated by the water column with a height of 1mm, that is, 1mmH2O= 10Pa. ( 1)

(3) Take the temperature rise of 40℃ as an example, and calculate the hot water output according to other parameters in the table. We hope to judge the meaning of "L" from this. Let the mass of hot water produced per minute be m, and the heat absorbed by water in 1min can be expressed as

Qi = cm (T2-T 1)...........................① ( 1)

On the other hand, according to the parameters given in the table, when the thermal efficiency is calculated as 80%, the heat absorbed by water in 1min is

Qi = = 4.93× 105J............② ( 1)

Solved by ① and ②.

M = = 2.9 kg ≈ 3 kg (2 points)

Judging from this, if the symbol between "3" and "/min" represents mass, its meaning should be "kg". Considering that the volume of 1kg water is 1L, this symbol must be the letter "l" (lowercase l), not the number "1". Therefore, the correct value and unit is 3L/ min. This conclusion can be confirmed by analyzing the temperature rise at 25℃ and 55℃. (2 points)

(4) by the relationship qi = cm (t2-t 1)

It can be seen that when the temperature rises to 25℃, the heat absorbed per minute is

Qi = 4.2×103× 5× 25j = 5.25×105j (1)

The heat produced by gas per minute is

=6. 17× 105J

Thermal efficiency η = = 85% (2 points)

Similarly, when the temperature rises to 55℃

Thermal efficiency = 75% (1 min)

When the temperature rises higher, it will lose more heat, so the thermal efficiency is lower.

Respondents: Master Liu 1234- Level 4 2- 16 13:20 rose to the first place.

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