Are there any questions or answers in the 17th National Junior High School Physics Application Knowledge Competition?

Examination questions of the 17th national junior middle school applied physics competition.

Precautions:

1. Please fill in the area, school, name and test number in the sealed line.

2. Write with a blue or black pen or ballpoint pen.

3. There are eight major topics in this paper, with full marks of 100.

4. Answer time: March 24th, 2007 (Saturday) 9: 30 ~11:10.

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

mark

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1. Only one of the four options given in the following multiple-choice questions is correct. Fill in the jade wood before the correct choice in the brackets after the question (2 points for each question, *** 10).

1. In order to ensure the safety during takeoff and landing, the following operations are correct during takeoff and landing.

( )

A. When taking off, the front wheel leaves the ground first, and when landing, the front wheel touches the ground first.

B The front wheel leaves the ground first when taking off, and the rear wheel touches the ground first when landing.

C the front wheel leaves the ground first when taking off, and the front and rear wheels touch the ground at the same time when landing.

D the front and rear wheels leave the ground at the same time when taking off, and touch the ground at the same time when landing.

Mobile phone has become a common communication tool in modern life. Ordinary mobile phones are equipped with devices that use vibration to remind people to "make a phone call". There is a kind of mobile phone that prompts "incoming call" by using a micro motor to drive the blades on the rotating shaft to rotate. When the blade rotates, the motor vibrates, which in turn drives the mobile phone to vibrate. In several shapes of blades shown in Figure 1, which one do you think can realize the above vibration function?

Figure 1:

3. In order to avoid the deterioration of vegetables in long-distance transportation, storage and other links and the destruction of nutrients in vegetables during high-temperature sterilization, vegetable processing enterprises often vacuum dehydrate vegetables to dehydrate them. From a physical point of view, the truth of vacuum dehydration is ()

A. The temperature in vacuum environment is extremely low, which can make the water in vegetables quickly solidify and sublimate, thus realizing dehydration.

B The temperature in vacuum environment is very high, which can make the water in vegetables evaporate quickly in a short time, thus realizing dehydration.

C. The air density in vacuum environment is very low, which can quickly increase the movement speed of water molecules in vegetables, thus realizing dehydration.

D. The air pressure in the vacuum environment is very low, which greatly reduces the boiling point of water and makes the water in vegetables vaporize quickly, thus realizing dehydration.

The thermos that people use to keep warm is shown in Figure 2. There are many long rubber protrusions on its surface, which are parallel to each other and very high. The main purpose of making this shape is ()

Figure 2:

A makes the hot water bottle beautiful and generous, and plays a decorative role.

B make the hot water bottle have the heat transfer functions of conduction, convection and radiation at the same time.

C. This protrusion has good elasticity, and it is easy to deform elastically under the action of external pressure, so as to prevent the thermos bottle from bursting under certain heavy pressure.

D, reducing the direct contact area between the thermos bottle and the human body, thereby reducing the heat release speed of the thermos bottle and realizing slow heat release.

Due to long-term siltation, the riverbed in the lower reaches of the Yellow River rises. Farmers along the river usually take water from the Yellow River to irrigate their farmland as shown in Figure 3. About this kind of diversion irrigation method, the following statement is wrong ()

Figure 3:

A. This irrigation method uses the principle of connector.

B. When in use, the nozzle at end B must be lower than the water surface at place A..

C. When in use, first fill the pipeline with water.

The greater the height difference h, the faster the water flows in the pipeline.

II. Fill in the blanks (every space 1 minute, *** 15)

1. In the ancient poem "Children Fishing", there is a saying that "passers-by use the topic to wave, and they are afraid of fish from afar."

(1) The fishing child just waved, but kept silent when asked by passers-by. This is because he knows that sound can spread not only in the air, but also in _ _ _ _ _ _ _.

(2) The reason why children wave _ _ _ _ _ _ (choose "Yes" or "No") and the fish can't hear it is _ _ _ _ _ _ _.

2. Last summer, Xiao Ming participated in the school's survival summer camp and learned a lot of knowledge and skills of survival in the wild. These include:

(1) Access to drinking water. As shown in Figure 4, put a large plastic bag on the twigs with dense leaves and tie the bag tightly. With the constant moisture in plants, a layer of water drops will appear on the inner surface of plastic bags after a period of time.

(2) Use shadows to identify directions. As shown in Figure 5, a straight rod is vertically inserted at the O point on the horizontal ground. Around noon, draw the trajectory of the shadow top of the pole on the ground by tracing points, and find out the point A closest to the O point on the trajectory, then the direction indicated by OA is _ _ _ _ _ _ _ (fill in "East", "West" and "North"), and the optical knowledge applied in this judgment is _ _ _ _ _ _ _ _ _.

3. When the photographer shoots graduation photo of the whole class with a fixed focal length camera and then shoots a bust of Xiaoming, the photographer should _ _ _ (fill in "increase" or "decrease") the distance between the camera lens and Xiaoming, and at the same time _ _ _ _ _ (fill in "increase" or "decrease") the distance between the camera lens and Xiaoming.

4. Incandescent bulbs that have been used for a long time will be covered with a layer of light black. This is because when the tungsten wire is heated, it will generate _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.

Snoely's oil storage tanks are shown in Figure 6. It is silvery white, with a large diameter and a short height (relative to the diameter), like a short fat man. Please answer:

(1) In these designs of oil storage tanks, "the whole body is silvery white" is _ _ _ _ _ _ _ _; "Larger diameter and shorter height" applies to _ _ _ _ _ _ _ _.

(2) There is also an automatic spraying device beside the oil storage tank. Every summer, especially at noon during the day, sprinklers are often used to spray water on oil storage tanks. This is mainly to use the larger characteristics of water and the heat absorption when water evaporates to supply _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.

Three. Answer the following questions briefly (4 points for each small question, 20 points for * * *)

1. Xiaohua has a cold and cough, and her mother bought her "Shuanghuanglian Oral Liquid".

Careless Xiaohua lost the special straw in the oral liquid box, so she had to take a drink straw and insert it into the bottle. As a result, she had a hard time "sucking" the potion out. Later, she found that the shapes of the two straws were different: the outer wall of the drinking straw was smooth, and the outer wall of the oral liquid straw was angular. The cross-sectional shapes of the two straws are shown in Figure 7. Please use your physical knowledge to explain why the two straws have different effects of "sucking" medicine.

Xiaoming wants to buy an electric stove to boil water. When he went to the store to buy it, he saw two specifications: 800W and1200 W. He thought: 800W has low power and saves electricity, so he planned to buy 800 W. Do you think his idea is reasonable from the perspective of energy saving? Why?

3. In the cold winter morning, car drivers often find white "breath" on the front windshield after getting on the bus, so they can get rid of the "breath" quickly by turning on the warm air; After the heavy rain in summer, the "breath" appeared on the windshield and window, which affected the safe driving, so the driver turned on the air conditioner for refrigeration, and soon the "breath" was removed. Why do drivers get the same effect by adopting different methods for the same phenomenon? Please explain it with your knowledge of physics.

Xiaohong bought a toy called "Blowing Bubbles" and found that sometimes bubbles can be blown out and sometimes they can't. In thinking, he had a question: what factors are related to the bubble? He guessed that the generation of bubbles may be related to the thickness of the pipe used to blow bubbles, so he designed and conducted experiments and recorded the following experimental results:

liquid soap

Pipe diameter/mm 3 5 10 20 50

Bubbles are getting easier and harder to avoid.

Please answer the following questions according to Xiao Hong's experimental records:

(1) What conclusions can be drawn from the analysis of the above experimental results?

(2) Please put forward two other conjectures to explain the factors that affect the bubble.

(3) Design a scheme to verify one of your conjectures.

5. As shown in Figure 8, it is an oil-immersed self-cooling transformer commonly used in transmission lines. The iron core and coil inside the transformer are immersed in transformer oil (a mineral oil, also called heat transfer oil). When the transformer works, the iron core and coil will heat up. This heat is mainly dissipated into the air through the heat transfer oil and metal pipe outside the transformer, so that the temperature of the iron core and coil will not rise too much to ensure the safe operation of the transformer. Please answer:

(1) Why is the radiator outside the transformer made into a pipe?

(2) There is an oil tank at the upper part of the transformer and an oil gauge at the side. The fuel gauge is a glass tube with open upper and lower ends, which is inserted into the fuel tank. Electricians can judge the amount of oil in the fuel tank by observing the height of the oil level in the glass tube. What is the main physical knowledge used in designing this device?

(3) From Figure 8, we find that the radiating pipes outside the transformer are distributed in the vertical direction instead of the horizontal direction. Why?

(4) Under normal circumstances, the heat transfer oil in the transformer oil tank is absolutely not allowed to be full. Why?

(8 points) Xiaoming bought a new100W electric blanket. He wanted to measure the resistance of the electric blanket with an ammeter and a voltmeter, so he connected the experimental circuit as shown in Figure 9. The voltage across the power supply is 6V, Rx is the resistance of electric blanket, and the maximum resistance of sliding rheostat is 20Ω. However, during the experiment, Xiao Ming found that no matter how to adjust the position of the contact P of the sliding rheostat, the indication of the voltmeter hardly changed, and he found that the circuit was connected correctly everywhere. Could you please analyze the reasons for this phenomenon? If the experimental equipment is not changed, how to connect the circuit can effectively change the voltage value at both ends of the electric blanket during the sliding process of the contact P.

Verb (abbreviation of verb) (10) is shown in figure 10, which is a schematic diagram of the automatic photoresistance counter installed in Liqun Commercial Building. Where A is the light source, B is the escalator driven by the motor and running at a constant speed, R 1 is the photosensitive resistor, R2 is the fixed resistor, and when there is light, R 1 = R2. Whenever a customer passes by the escalator and blocks the light from A to R 1, the resistance value of R 1 increases and the counter counts once. Please answer:

1. When the customer on the escalator blocks the light from A to R 1, what will happen to the voltage across R 1? How does the power of R 1 change?

2. If the escalator is known to be fully loaded, the distance between two adjacent customers is 50cm, and the running speed of the escalator is 1m/s ... Find the time required for the counter to count 10 1 time.

3. If the escalator occupancy rate is 20% in a certain period of time, try to find out the average passenger flow on the escalator in this shopping mall during this period. (Passenger flow refers to the number of customers passing by per unit time)

6.( 10) "The pressure acting on a closed liquid can be transmitted in all directions by the liquid under the condition of constant size", which is Pascal's law. In the communication device shown in figure 1 1, if the mass of the piston and the gravity of the liquid itself can be ignored, it can be inferred from Pascal's law that the force acting on the large and small pistons has the following relationship with the area of the large and small pistons:

According to this relationship, if the area of the small piston is small, a small force is added to the small piston, and a large force can be obtained on the large piston. "Hydraulic jack" is made according to Pascal's law.

Figure 12 shows the cross section of the hydraulic jack. It is a regular maintenance tool for transportation machinery such as automobiles. As long as a small force f is applied to the lever, a car can be jacked up, which is convenient for replacing and repairing tires. If the large piston area of the illustrated jack is 40cm2 and the small piston area is 5 cm2, OA= OB on the lever. Please answer:

1. In use, it is found that although the heavy object can be lifted by pressing the lever, the heavy object will fall off after releasing the lever and cannot be held for a long time. This indicates that a part of the illustrated jack is damaged or lost. Please draw a part and fill it in the corresponding position, so that the lifted weight will not fall down again (just draw a schematic diagram on Figure 12).

2. If the mechanical efficiency of the repaired hydraulic jack is 80%, when it is used, it is assumed that the big piston is just against the vertical line of the center of gravity of the heavy object. If the weight of 1t is increased by 3cm within 1 min, what is the average power consumed by the maintenance personnel and the force applied to the B end of the lever? (take g = 10n/kg)

Seven. (13) There are two households A and B in a hospital. The original power supply line in the hospital adopts aluminum core rubber insulated wire with a cross-sectional area of 2.5mm2. After entering the hospital, it reaches the first household through 25m from the terminal, and then reaches the second household through 25m. The rated power of each household is 2kW. In order to improve the maximum safe power consumption of users, it is necessary to "increase the power capacity" and increase the rated power of each household to 4kW. After the expansion, the distribution of lines in the hospital remains unchanged, but the power supply lines are replaced by copper-core rubber insulated lines. The following table lists the safe current carrying capacity of copper wires with different cross-sectional areas at room temperature (that is, the maximum safe current when electrified for a long time).

Conductor cross-sectional area s/mm2 Safe current carrying capacity of copper-core rubber insulated conductor I/A

2.5 28

4 37

6 47

10 68

Assume that all appliances in two households are pure resistance appliances, and the rated voltage of each appliance is 220V, ignoring the resistance of indoor wires. And the voltage of the terminal is always kept at 220V V after entering the hospital. Try to answer the following questions:

1. Draw the circuit diagram of hospital power supply and electricity consumption.

2. The calculation shows that, on the premise of practicality and economy, in order to "increase the power capacity", the power supply in the hospital

What kind of copper wire should be used for the line?

3. If the resistance per meter of the selected copper conductor is 4.25×10-3 Ω, when two users use "220KW" electrical appliances at the same time, what is the actual electric power obtained by household B?

8.( 14) Figure 13 is a common electric bicycle. Please charge the battery on your bike before using it. When riding, the battery supplies power to the motor on the car, and the motor provides power to the car. The following table shows some main technical parameters of this brand of electric bicycles.

The maximum speed is ≤ 30km/h, and the continuous driving mileage on one charge is 50km.

Battery 36V/ 10Ah

The charging time of lead-acid battery is 8h.

Power consumption of 0.6kW on a single charge? H motor efficiency 80%

The vehicle mass is 40kg, and the maximum ride noise is ≤62dB.

Please answer:

1. What is the physical meaning of "336V/ 10Ah" in the technical parameter table?

2. If a person with a mass of 70kg rides an electric bicycle at a constant speed of 6m/s on a horizontal road, the resistance is 0.02 times of the total weight of people and vehicles, and g = 10N/kg. Find the work done by the motor to the bicycle after driving for 20min minutes and the current passing through the motor coil.

3. If the motorcycle 10km consumes 2.5L, and the oil price is about 5. 1 yuan /L, please take a photo.

Is the electricity charge about 0.5 yuan/kW? H, please explain by calculation which is more economical to use electric bicycle or motorcycle.

Please compare the environmental pollution of electric bicycles and motorcycles from the perspective of environmental protection.

5. In transportation, "passenger efficiency" is often used to reflect a certain efficiency of vehicles. "Passenger efficiency" refers to the product of the number of passengers per unit energy consumption and the transportation distance, that is, passenger efficiency = number of people × distance/energy consumption. One person can ride an electric bicycle for 30km, and the energy consumption is 1mj( 106j), while four people can ride an ordinary car 100km, and the energy consumption is 320MJ. What is the passenger efficiency ratio between electric bicycle and this car?