Physics competition questions

17 national junior high school applied physics competition questions

note:

1, please fill in the stamped area, the name of the school and the number of candidates.

2。 Written with a blue or black pen or ballpoint pen.

3。 Full score 100 test paper ***8 big questions.

Respondent time: Saturday, March 24th, 2065438 +00, 9:30 am to 1 1: 00, 10.

Question 12345678***

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Of the four options of multiple-choice questions, only one is correct, and the correct option is in brackets after mom fills in the blanks (2 points for the paper, *** 10).

1。 In the process of taking off and landing, in order to ensure safety, the following operations are correct.

()

A. When taking off, the front wheels land first, and when landing, the front wheels land.

B. The front wheels take off first, and the rear wheels land.

C the front wheels leave the ground before takeoff and the rear wheels touch the ground before landing. At the same time,

D before and after take-off, the wheels leave the ground and land at the same time, and the rear wheels land.

Mobile phone has become a common communication tool in modern life. Generally, mobile phones use vibration to remind people to "shout". There is a telephone prompt that when the blade rotates with the blade driven by the driven shaft of the micro motor, the motor will vibrate accordingly, which will lead to the vibration of the mobile phone. Figure 1 shows several shapes that can realize vibration function ()

Figure 1

3。 In order to avoid deterioration and high-temperature sterilization, vegetable processing enterprises often dehydrate vegetables in vacuum during long-distance transportation and storage, and dehydrated vegetables become the destruction of nutrients in rotten vegetables. The Truth of Vacuum Dehydration ()

A. When the temperature of vacuum environment is low, vegetables quickly solidify and sublimate water to realize dehydration.

B. The high temperature in the vacuum environment makes the vegetables in the water evaporate quickly in a short time, thus realizing dehydration.

C. Low air density in vacuum environment can quickly increase the movement speed of water molecules in vegetables and realize dehydration.

D. The pressure in the vacuum environment is very low, which greatly reduces the boiling point of water, so that vegetables can be rapidly vaporized in water to realize dehydration.

4。 The hot water for heating bottles shown in fig. 2 has many strips with rubber protrusions on their surfaces. These protrusions are parallel to each other, and the height of the protrusions is very large. Its main purpose is to make this shape ().

A. beauty makes the thermos bottle have decorative function.

B it has the functions of conduction, convection and radiation heat transfer.

. This prediction has good flexibility and is easy to deform elastically under external pressure to prevent the thermos bottle from bursting under the weight of irrigation water in some cases.

D. reduce the direct contact area of hot water bottles? Human body, hot water bottle, reduce the heating speed and slow down the heat release.

5。 Due to long-term siltation, the riverbed in the lower reaches of the Yellow River rises. Rivers are usually as shown in Figure 3, and the water from the Yellow River irrigates farmers. The following statement about irrigation is wrong ()

Answer: This irrigation method is to use joints.

B. the principle of the nozzle on the b side, the water quantity on the a side must be less than.

C. Use a tube filled with water first.

what's up D the greater the height difference, the faster it will be in the running water pipeline.

/a & gt；

Secondly, fill in each blank (1, *** 15).

The poem "Children Fishing" asks passers-by who waves and is afraid of fish.

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

(2) It is inaudible for children to wave _ _ _ _ _ _ _ (optional "yes" or "no") fish, because _ _ _ _ _ _ _ _.

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

(1) Access to drinking water. Figure 4. Tie the mouth of a big plastic bag with leafy branches. _ _ _ _ _ _ and _ _ _ continuous aquatic plants, with the passage of time, a layer of water droplets appeared on the inner surface of plastic bags.

(2) Determine the direction of using shadows. As shown in fig. 5, a straight rod will be vertically interpolated at point o on the horizontal ground. At noon, the tie rod at the top uses the method of tracking the shadow of points on the ground to identify the direction _ _ _ _ _ _ _ indicated by point A and point OA on the track ("East", "West" and "South" directions can be selected "North"), and the application of this judgment optical knowledge is _ _ _ _ _ _ _ _.

3。 The photographer took another class of graduation photo with a fixed focal length camera and gave it to Xiaoming's classmates. Then according to the photographer should _ _ _ _ (fill in the distance. "Increase" or "decrease"), the distance between the camera lens and classmate Xiao Ming, _ _ _ _ (fill in "increase" or "decrease") to the last film lens.

4。 Covered with a layer of black light for a long time, because the tungsten filament is heated to the incandescent light bulb, the phenomenon of _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

5。 As shown in Figure 6, the oil storage tank is covered with silvery white, with a large diameter and a short height (relative diameter), like a stout person. Please answer:

(1) The design of the storage tank is "covered with silvery white" and marked with _ _ _ _ _ _ _ _; Large diameter, high, short, _ _ _ _ _ _ _ _ _.

(2) The automatic sprinkler also installed beside the oil tank is generally used to spray water from the sprinkler and the oil storage tank every summer, especially at noon on a certain day. Its main feature is that it adopts the form of _ _ _ _ _ _ _ _ _ _ _ _

The short answer (file 4, ***20 points) is as follows.

Xiaohua coughed and caught a cold. My mother bought me her Shuanghuanglian oral liquid.

Careless Xiaohua lost the special straw in the oral liquid box and brought a drink straw into the bottle, so it took a lot of effort to "suck" the medicine out. Later, she found that the shapes of two kinds of straws are different: one is a beverage straw with smooth outer wall, and the other is the cross-sectional shape of the oral liquid straw rib as shown in Figure 7. You can use physical knowledge to explain why two straws "suck" drugs.

Xiaoming bought an electric stove to boil water. He went to the store and bought two specifications, 800W and1200 W. He thought: 800W is better. What do you think of his idea from the perspective of energy? Why?

In the winter morning, the driver on the train often finds that there is a white smell on the front windshield, so he turns on the warm air and can get rid of "breathing" soon; In summer, after the heavy rain, the "breathing" on the windshield window can drive safely, allowing the driver to turn on the air conditioner and refrigeration. Soon, "breathing" is to get rid of the same phenomenon. Drivers use different methods, but the results are the same. Why? Explain what you have learned in physics.

4。 Xiaohong bought a toy called "Blowing Bubbles" and found that sometimes she blows bubbles, and sometimes she doesn't. Thinking, he has a question: What factors are related to this bubble? He guessed that the generation of bubbles may be related to the thickness of the bubble blowing tube. He designed and conducted experiments and recorded the results as follows:

Liquid soap, pipe diameter/mm 3 5 10 20 50

Bubbles that are easy to produce are easier to produce and more difficult to produce.

Please answer the following questions in the small flood recorded in the experiment:

(1) What is the conclusion after analyzing the above experimental results?

(2) Two other conjectural factors affecting bubbles are proposed. & ltBR/(3) Design a program to verify your guess.

Fig. 5 shows an oil-immersed self-cooling transformer used in the transmission line in fig. 8. When adding transformer core, the coil is immersed in the core of transformer oil (mineral oil, heat transfer oil, etc.). When the coil heat exchanger works, the heat mainly flows to the atmosphere through the heat conduction oil and the metal pipe outside the transformer, so that the temperature of the iron core and the coil will not rise too much, thus ensuring the safe operation of the transformer. Please answer: Why?

(1) Tubular radiator outside transformer?

(2) In the upper part of the transformer oil tank, the fuel gauge is nearby. The fuel gauge is one of the lower ends of the opening, and the glass tube is inserted into the water tank. Determine how much oil is in the fuel tank by observing the height of the oil level in the glass tube. Excuse me: what is the design of electrician? This device uses physical knowledge?

(3) From Figure 8, we find that the cooling pipes outside the transformer are distributed vertically, not horizontally. Why?

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

4。 (8 points) Xiaoming bought a new electric blanket of100W, and wanted to measure the resistance of the electric blanket with an ammeter and a voltmeter. The experimental circuit connected left and right is shown in Figure 9, in which the power supply voltage 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 number displayed by the voltmeter hardly changed, no matter whether all the circuits were connected correctly or not. What are the reasons for this phenomenon? If the experimental equipment is not replaced, how to connect the circuit contact P to effectively change the voltage at both ends of the electric blanket during sliding?

Verb (abbreviation of verb) (10) The schematic diagram of the automatic counter is as shown in figure 10, which is the photosensitive resistor installed in Liqun Commercial Building. The escalator runs a unified light source driven by a motor, where B is a photosensitive resistor R 1 and R2 is a constant resistor. When the escalator customer passes, when the light is directed to R 1 and prevented from increasing by the resistance value R 1 of A, the counter counts once. Please answer:

1。 When the voltage across the photoresistor R 1 changes, what is the power change of the customer's A R 1 R 1 on the escalator?

2。 It is known that in a fully loaded escalator, the distance between two adjacent customers is 50 cm, and the running speed of the escalator is1m/s. The time required to find the counter is 10 1.

3。 The running time of the escalator in a certain period of time is multiplied by the daily average traffic flow, and the load rate is 20%. In the meantime, the escalators in the mall. (number of customers after flow unit time) BR/& gt；;

6. (10 minute) The pressure in a closed liquid can be the same liquid. This law is called Pascal's law by "all directions". For the communication shown in figure 1 1, if the effect of gravity on the quality of the piston and the liquid itself can be ignored, it can be deduced according to Pascal's law that the force acting on the small piston and the area of the small piston is as follows:

=

According to this relationship: if the area? The small piston is smaller, so the small piston plus a relatively small force can get more force from the piston. Hydraulic jack is based on Pascal's law. As shown in figure 12.

This is a sectional view, hydraulic jack. It is suitable for transportation machinery such as automobiles. With a maintenance tool and a little force, the F-bar stands on the top of the automobile, and it is easy to replace and repair tires. If the icon jack piston area is 40 square centimeters? Yes, the area of the small piston is 5 square centimeters, and OA = OB lever. Please answer:

1。 You can put a heavy object on it when you are depressed, but you can stand for a long time without putting a heavy object when you lose weight. 10 A part of this icon jack is damaged or missing. You draw it in a proper position, so that top-heavy objects will not fall down and draw a schematic diagram, and the diagram 12 can be partially filled. about

The mechanical efficiency installed on the hydraulic jack is 80%. When in use, it is assumed that the big piston is only at the top of the vertical line of the center of gravity of the weight. If the weight of 1 ton is 3 cm within 1 minute, what is the rod force maintenance being processed in Terminal B based on the average power consumption of one person? (at G = 10N/kg)

/a & gt；

7. (13) What is the cross-sectional area of the initial power cord for residents in hospitals A and B? 2.5 mm square aluminum core rubber insulated cable from the terminal to the hospital after 25 meters first arrived at the account, 25 million arrived at the B account. The rated power of total household electricity consumption is 2KW. Maximum protection, in order to increase users' electricity consumption and electricity consumption, the rated power of total household electricity consumption can be increased to 4 kilowatts. After the expansion to the hospital, the distribution of lines is the same, and the only power cord is replaced by copper-core rubber insulated wire. The following table lists? Safe current carrying capacity of copper conductor with different cross-sectional areas at room temperature (that is, when the maximum safe current is long when electrified).

Safe bearing capacity of copper-core rubber insulated conductor with wire diameter and cross-sectional area of S/mm2/A 2.5 28

37

6 47

10 68 & lt； BR/ Assume that two devices are purely resistive appliances, and the rated voltage of each appliance is 220V, so the indoor line resistance of users can be ignored. After arriving at the hospital, the terminal voltage should be kept at 220V V. Try to answer the following questions:

Draw the circuit diagram of power supply and power supply field.

The calculation shows that the ranking of practical economy is based on the power supply capacity of hospitals.

Should copper wire be used?

3。 The resistance per meter, if the copper wire is 4.25×10-3 Ω, then what is the actual electric power of account B that users A and B can use for capacity expansion?

a & gt

Eight (14) diagram 13 is a common electric bicycle, which should be charged before the first use. Riding, battery-driven electric vehicles, power of electric vehicles. The following table is the main technical parameters of this brand of electric bicycles.

Maximum speed ≤ 30km/h, 50km/h, continuous mileage on a single charge.

Single charge battery 36V/ 10Ah

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

Power consumption 0.6 kw·h motor efficiency 80 Please answer: 40 kg maximum riding%

Vehicle noise quality ≤62 dB

What is the physical meaning of the technical parameter table 336V/ 10Ah?

2。 If a person with a mass of 70kg rides a bicycle at a constant speed of 6m/s on the flat ground, the resistance is 0.02 times of the total weight of people and vehicles, and G = 10N/kg. Qualification: The motor driven by bicycle works, and the current passes through the motor coil for 20min.

3。 Every 2.5L 10 km of motorcycle fuel, the oil price is about 5. 1 yuan/lighting electricity fee is about 0.5 yuan /kW? H By calculating which economy uses electric bicycles and motorcycles.

4。 From the environmental point of view, the environmental pollution of electric bicycles and motorcycles is compared.

5。 Transportation, commonly used passenger transport efficiency ",to reflect a performance of transportation," passenger transport efficiency, unit energy consumption and the number of passengers corresponding to products other than transportation, that is, the number of effective passengers = × distance/energy consumption. A person riding an electric bicycle can travel 30 kilometers, with energy consumption 1MJ( 106J). What is the energy efficiency ratio of an electric bicycle passenger car with four people, energy consumption of 320MJ and driving speed of 100 km?