The 23rd "International Science and Peace Week" national primary and secondary school students (Jiangsu area) "Shenghong" Cup Golden Key Science and Technology Competition for senior high school indiv

The 23rd "International Science and Peace Week" national primary and secondary school students (Jiangsu area) "Shenghong" Cup Golden Key Science and Technology Competition for senior high school individual preliminaries. The 23rd International Science and Peace Week "Shenghong" Cup Golden Key Science and Technology Competition for Primary and Secondary School Students (Jiangsu)

Answers to individual preliminary contest questions in senior high school

(out of 19, including 6 additional questions)

1. Knowledge questions (out of 3)

(1), multiple-choice questions (1 point for each question, ***15 points)

1 2 3 4 5 6 7 8 9 1 11 12 13 14 15

A D A B A D A C A D B

(2), true or false questions (1 point per question, ***15 points)

1 2 3 4 5 6 7 8 9 1 11 12 13 14 15

×××××××××××××××××××××××

Second, comprehensive application questions (***2 questions, 2 points for each question, 4 points for * *) (below) ① The fundamental reason of table tennis rotation is that the line of action of the ball does not pass through the center of mass of the ball. When the racket hits the ball forward and upward at a certain inclination, the force given to the ball is the resultant force of tangential friction (making the ball rotate) and impact force (making the ball translate). The direction of the resultant force does not point to the center of the ball (center of mass), but makes the ball move forward and upward, at the same time, rotates around the horizontal horizontal axis to form a topspin.

② The trajectory of the ball in the air, including the trajectory after falling on the opponent's desktop and jumping up (as shown in the figure), is an obvious "banana ball" curve, especially in the falling stage, with greater curvature.

③ When the topspin is in air movement, it is subjected to three forces: one is air resistance, which is opposite to the ball's forward direction; The second is gravity, which points to the center of the earth; Third, when the ball rotates and moves forward, the air velocity on the upper side of the ball is smaller and the air velocity on the lower side is larger. According to Bernoulli's principle, the pressure on the top is larger, and the pressure on the bottom is smaller. The force generated by the pressure difference between the top and bottom is perpendicular to the direction of the ball. Under the combined action of these three forces, a banana-shaped trajectory is formed, and the curvature radius of the curve in the falling stage is smaller.

Scoring criteria:

1. Correctly explain the reason of topspin rotation; (7 points)

2. Describe the trajectory of the ball correctly; (6 points)

3. Correctly explain the reasons for the formation of the ball trajectory. (7 points)

2. Answer: As we know, an atom is composed of a nucleus and electrons revolving around the nucleus, and the nucleus is composed of positively charged protons and uncharged neutrons. If uranium -235 is bombarded with neutrons, the uranium nucleus will split into two new nuclei with smaller mass, and 2 ~ 3 neutrons and other rays will be released, and huge fission energy will be released at the same time. The released neutrons bombard other uranium -235 nuclei, which will cause new nuclear fission, which will generate new neutrons and fission energy, and so on, forming a chain reaction. This chain reaction can generate about 1 generations of neutrons in one second, which can release huge nuclear energy in a very short time. In the nuclear reactor, in order to control the nuclear reaction speed, it is necessary to use control rods made of cadmium and other materials to absorb neutrons to control the number of neutrons. Water is used as moderator and coolant, and the moderator is used to slow down the neutron speed and effectively control the nuclear reaction speed; Coolant (water) converts fission energy into heat energy of steam, then into mechanical energy of turbine, and finally into electric energy.

Japan's Fukushima nuclear power plant uses a boiling water reactor. Its main features are as follows: First, the steam that drives the steam turbine is directly generated in the reactor core. After being separated and dried by the steam-water separator at the top of the reactor, the steam is led out by the pipeline and sent to the turbine to drive the generator to generate electricity. The steam from the turbine is condensed and treated, and then sent back to the core for heating. The circulating water here is both a coolant for fission energy and a moderator for neutrons, so it contains radioactive substances. Second, because the upper part of the reactor is occupied by the steam-water separator, the control rod can only be placed in the lower part of the reactor (the control rod is generally placed above the reactor, and once an accident occurs, the reactor can be automatically stopped by the gravity of the control rod), and it must be pushed up by other power and inserted into the core to control the nuclear reaction speed.

on the afternoon of March 11th, after the earthquake, the control rod was inserted, and the reactor was safely shut down, so the thermal power of the core quickly decreased. At this time, as long as the cooling water can be continuously injected and cooled, the core will be fine. However, the earthquake destroyed the external power grid and the external power supply was unavailable; The emergency diesel engine began to generate electricity, driving the water pump to inject water into the core, but a few minutes later, the tsunami came, the engine room was flooded and the diesel engine could not be used; Although there is a battery, its capacity is small; However, the generator of the mobile diesel engine shipped later is incompatible with the interface of the power station. All the measures failed, the water pump could not be started, and water could not be injected into the core for cooling. However, the core fuel rods are exposed, the residual heat is constantly generated, and the temperature and pressure in the containment continue to rise. At high temperature, water or steam reacts with zirconium in the protective shell of the fuel rod to produce zirconium oxide and a large amount of hydrogen. In order to prevent the overpressure explosion of the reactor pressure vessel, the operator released steam into the plant to relieve pressure. Because a large amount of hydrogen contained in steam is mixed with oxygen, it will explode strongly at high temperature or open flame, destroying the reactor building, resulting in the leakage of steam containing radioactive iodine and cesium.

scoring principle: due to the different information searched by each person, the content of the expression may be different, even contradictory, and it can be scored according to the specific situation in four grades: 2, 15, 1 and 5.

3. Divergent thinking questions (2 points)

Reference answers: ① All kinds of household appliances such as cookers, water heaters, heaters and electric blankets must be installed and used correctly in strict accordance with the specified requirements; ② Know different fires and use different fire extinguishing methods; (3) indoor heaters and open flames should be kept away from flammable items; (4) when people are not at home, turn off the fire source and heater power; ⑤ In case of gas and natural gas leakage at home, you can't make a phone call, turn on the electric light, turn on the exhaust fan and other household appliances, and you can't forcibly collide with metal objects, so as not to cause sparks and sparks, which may lead to explosion and fire; ⑥ The load of household appliances cannot be overloaded; ⑦ The fuse can't be replaced by copper wire or iron wire, so as to avoid being unable to fuse and catch fire when the load exceeds; 8 smokers should not smoke in bed, so as not to accidentally ignite flammable items on the bed; Pet-name ruby don't let children play with fire; Attending to remember the fire alarm telephone number 119, and call the police in time when there is a fire.

Scoring standard:

1. As long as it is effective for fire prevention and disaster reduction, it is correct;

2. 2 points for each correct answer, with a total score of no more than 2 points.

IV. Composition questions (4 points)

Grading principle:

1. Be positive and relevant; (8 points)

2. Unique, profound and innovative opinions; (1 points)

3. The article has a rigorous structure and clear levels; (8 points)

4. The written expression is concise and accurate; (8 points)

5. The text is not less than 8 words. (6 points) < P > V. Research study (2 points) < P > Reference answer: < P > 1. General practice of steaming eggs: knock fresh eggs into a bowl → stir well → add appropriate amount of water (or fresh milk) → stir well → put them in a pot and steam them out → add sesame oil, soy sauce and other seasonings.

2. some steamed eggs are cooked in boiling water and some are steamed on a steamer. now, take water-proof cooking as an example. The prepared egg liquid is boiled in boiling water. Except a small amount of radiant heat, the heat for cooking eggs mainly comes from two aspects: one is to transfer the heat of boiling water to the egg liquid through the heat conduction of the bowl wall, and the egg liquid is evenly heated through the convection of the egg liquid; Second, by condensing steam on the upper surface of the egg liquid, the released heat (latent heat of vaporization) heats the egg liquid. If the wall of the bowl is thick and the heat transfer is slow, the temperature on the upper surface of the egg liquid will be higher than that under the liquid surface, and there will be no convection in the egg liquid in the bowl. At this time, the heat energy of steamed eggs mainly comes from the heat transmitted downwards by the latent heat released by the steam condensation on the upper surface.

3. To steam a bowl of good eggs, at least four points should be paid attention to: ① The ratio of eggs to water or milk is appropriate (generally 1: 1) and the mixture should be evenly stirred. If there is too much water (or milk), the steamed eggs will not form; Too little will look old and hard. (2) Use bowls with good heat conduction of bowl wall materials, or use shallow dishes with a depth of 3 ~ 4 cm to ensure that the egg liquid is uniform in thickness and heated evenly, so that there will be no difference in raw and cooked food. If the bowl wall is thick, the heat transfer is slow; The bowl is deep, which makes the egg liquid deep and thick. At this time, the egg liquid is heated mainly by the latent heat released by the condensation of steam on the upper surface. If there is no artificial stirring in time, the steaming time will be very long. Then the steamed eggs will appear dry, wrinkled, porous and old, while the bottom may not be ripe. ③ Grasp the time. The steaming time is related to the amount of egg liquid and the bowl used. If the time is too long, in addition to dry wrinkles, porosity and aging, sometimes dehydration will occur. Such steamed eggs are not only ugly in appearance, but also bad in taste; (4) steamed eggs should be cooked with medium and small fire, not with big fire, or they will be steamed easily.

note: be careful about the safety of using fire, electricity and contact with boiling water and steam, and ask parents for supervision if necessary.

Scoring principle:

1. Finish the research and write the report as required; (8 points)

2. Be able to correctly explain the heat transfer process; (6 points)

3. The analysis is reasonable and the conclusion is correct. (6 points)

VI. Computer design questions (2 points)

Scoring criteria:

1. Complete picture elements (theme name, pictures or decorations serving the theme, CHINA Post, China, face value, serrated edges around); (6 points)

2. Rich in imagination and innovative; (8 points)

3. Rich colors, fresh and clean pictures. (6 points)

VII. Hands-on Practice Question (2 points)

Reference answer:

If this container is placed horizontally on the train, when the train travels to the right in the horizontal direction with acceleration A, the liquid level in the container will become inclined (as shown in the figure), and the greater the acceleration, the greater the inclination angle θ. In order to find the relationship between a and θ, we can imagine taking a very small horizontal water column in the water, with the cross-section area of △S, the length of L, the height of the left center from the water surface of H, and the right surface of which is consistent with the water surface. The force that makes this water column make an acceleration movement to the right in the horizontal direction is the pressure difference on its two sides, that is, < P > (pLeft-pRight)? △S=ma

ρgh? △S=ρL△S? a

gh= La

a=hg/L=g? Tanθ

When manufacturing a container, the length of the container is 2cm, and the horizontal plane is scale. Let g ≈ 1m/sec 2, L = 1cm, and H is the height of the left center from the water surface, then a=h m/sec 2, that is, the liquid level at one end of the container rises by 1cm, which means that the acceleration of the train is 1m/sec 2, and it rises by h cm, and a=h m/sec 2.

Scoring standard:

1. Make an accelerometer as required, with a maximum score of 8;

2. Can establish a correct mathematical model, with a maximum score of 12 points.

Sorry, the preliminary contest has passed, so I'll give you the answer.