Excuse me, who has the questions and answers of the rematch of the 17th National Junior High School Applied Physics Competition? Urgent! Please give me more help.

The 17th National Junior High School Applied Physics Competition (with answers) The 17th National Junior High School Applied Physics Competition (with answers)

Precautions:

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

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

3. This paper has eight points, with the full score of 100.

4. Answer time: March 25th, 2007 (Sunday) at 9: 30-11:100.

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

mark

chessman

Scoring reviewer

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

1. In order to ensure the safety when the plane takes off and lands, when the plane takes off and lands,

The correct of the following operations is ()

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. What do you think is () that can realize the above vibration function in the knife blade in figure 1?

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 ()

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

B. Hot water bottles can have conduction, convection and radiation at the same time.

Heat transfer function

C. this kind of protrusion has good elasticity and works under external pressure.

Elastic deformation is easy to occur under the cutting tool to prevent it from being deformed under some heavy pressure.

The hot water poured in will burst the hot water bottle.

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 Profile of Farmland Irrigation

A. This method of water intake irrigation uses the connector principle. B. When in use, the nozzle at end B must be lower than the water surface at place A..

C. When in use, fill the pipeline with water. D 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. It's all because of him.

You should know that sound can spread not only in the air, but also in _ _ _ _ _ _ _.

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

Xiaoming participated in the school's survival summer camp last summer.

Ling Ying learned a lot of knowledge and skills for survival in the wild.

Yes These include:

(1) Access to drinking water. As shown in fig. 4, it is made of large plastic

The material bag is sleeved on the dense branches of the leaves and tied tightly at the mouth of the bag.

With the decrease of water in plants

After a period of time, the inner surface of the plastic bag will

A layer of water droplets appeared.

(2) Use shadows to identify directions. As shown in fig. 5,

Insert a straight rod vertically at point O on the horizontal ground. Around noon, draw the running track 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 track, then the direction indicated by OA is the direction of _ (fill in "East", "West", "South" and "North"). The optical knowledge used for 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 _ (fill in "increase" or "decrease") the distance between the lens and the film.

4. Incandescent bulbs that have been used for a long time will be covered with a layer of light black. This is because the tungsten wire is heated to produce _ phenomenon, and tungsten vapor appears, which produces _ on the inner wall of the bulb.

As shown in Figure 6, the oil storage tanks in Snoely are silvery white.

Bigger in diameter, shorter in height (relative to diameter), like a short fat man.

Please answer:

(1) In the design of these oil storage tanks, "all silvery white" is

For; "Larger diameter, lower height" is to

.

(2) An automatic nozzle is also installed beside the oil storage tank. Every summer,

Especially at noon during the day, spray nozzles are often used to spray water to the oil storage tanks, mainly to prevent the spontaneous combustion of oil by using the large characteristics of water and the heat absorption characteristics when water evaporates.

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; In summer, after the heavy rain, it will also appear on the windshield. "Breathing" affects safe driving, and the driver turns on the air conditioner for refrigeration, and soon "breathing" is also lifted. 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:

(l) 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, the 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 the metal pipe outside the transformer, so that the temperature of the iron core and the coil will not rise too much, ensuring the safe operation of the voltage transformer. Please answer:

(l) Why is the radiator outside the transformer tubular?

(2) There is an oil tank on the upper part of the transformer and oil on the side.

Scale. The fuel gauge is a fuel tank with both upper and lower ends open.

The glass tube is here. Electricians can judge by observing the height of the oil level in the glass tube.

How much oil is in the tank? 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 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, the voltage across the photoresistor R 1 will

What changes have taken place? How does the power of R 1 change?

2. If it is known that when the escalator is fully loaded, two adjacent ones

The distance between customers is 50cm, and the escalator runs at high speed.

The degree is 1 rn/s, find a counter to calculate 10 1 times, if necessary.

Time.

3. If the occupancy rate of escalators within a certain period of time

20%, try to find the escalator in this shopping mall within this time.

What is the average passenger flow in the world? (Passenger flow refers to the unit hour.

Number of customers passing by)

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, then 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.

Figure. Is a regular maintenance worker of transportation machinery such as automobiles.

As long as a small force f is applied to the lever,

You can jack up the car for easy replacement and repair.

Cut the tire. If the illustrated jack has a large piston area

It is 40cm2, and the small piston area is 5cm2, which is on the lever.

OA= OB. 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 = 10 n/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. Through calculation, under the premise of practicality and economy, what kind of copper conductor should be selected for hospital power supply lines to "increase power capacity"?

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?

Eight, (14 points) Figure 13 is a common electric bicycle. Before use, charge the battery in the car. 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 technologies of this brand of electric bicycles.

Parameters.

The maximum speed is ≤30kn/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 "36V/ 10Ah" in the technical parameter table?

2. If a person with a mass of 70kg rides an electric bicycle at a constant speed of 6 m/s on a horizontal road.

The resistance is 0.02 times of the total vehicle weight, taking 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 100km consumes 2.5L, the oil price is about 5. 1 yuan /L, and the lighting electricity fee is 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. A person riding an electric bicycle "consumes 1MJ( 106J) energy and can travel 30km, while an ordinary car with four people can travel 100km with 320MJ energy. What is the passenger efficiency ratio between electric bicycle and this car?

Reference Answers and Scoring Criteria of the 17th National Junior Middle School Applied Physics Competition

Description:

1. Except for multiple-choice questions, the provided reference answers are not necessarily unique and correct. For those different solutions, the correct one will get the same score.

2. The grading standard is only given according to an idea and method. In the process of marking papers, there will be various situations, and specific treatment methods can be formulated according to the spirit of this scoring standard, but there should be no major deviation from this scoring standard.

3. Questions and answers or calculation questions are graded in a step-by-step manner. In the grading standard, (1) and (2) are often written ... The formula here is used to represent the steps. If the candidate does not write this formula, but embodies this step in the process of writing expression or later problem solving, the score is the same. If you don't write any formula or text description and only give the final result, you can't score.

4. The numerical results in the reference solution are given according to the operation requirements of significant figures, and there is no requirement for candidates. Don't deduct points because of errors in valid figures.

5. In the final award, if the number of people with the same score exceeds the number of winners, it is difficult to select, and the papers to be selected can be judged by adding points. The basic basis for judging extra points is:

(l) The method or principle used is not what the textbook says, which is innovative and deserves extra points;

(2) The method is simple, and extra points should be given:

(3) Put forward a variety of correct solutions, which should be supplemented;

(4) The test paper is clear and can make full use of mathematical tools, so extra points should be given.

The implementation of the above-mentioned projects shall be stipulated by the competition leading group (the province decides to uniformly allocate the reward places, and the prefecture and city decide to allocate the reward places).

First, multiple-choice questions (2 points for each small question, *** 10)

1 .B 2。 C 3。 D 4。 D 5。 A

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

1.( 1) (1 min) water

(2) When (1) waves (1), the vibration frequency of the hand is very low, and the fluctuation frequency is also very low, which is out of the hearing range of the fish.

2.( 1) (1) evaporation (l) liquefaction; (2)( 1) South (1) light travels in a straight line.

(1) Decrease (1) Increase

4.(L) Sublimation (1) Ninghua

5.( 1) (l) Try to reflect sunlight (1) to stabilize the oil tank and increase the volume.

(2)( 1) specific heat capacity (1) cooling.

Three, short answer questions (4 points for each small question, ***20 points)

1.(4 points) Reference answer:

After the straw is inserted into the medicine bottle, because the outer wall of the drinking straw is smooth, it is in close contact with the rubber bottle cap of the medicine, and air cannot enter, so it is difficult to "suck" the medicine ....................................... to give 2 points.

The outer wall of the liquid medicine straw is angular (or uneven), which is beneficial to the entry of air. Under the action of atmospheric pressure, the liquid medicine is pressed into the mouth, and ....................................... scores 2 points.

2.(4 points) Reference answer

When an electric stove is used, it consumes electric energy. Whether to save electricity can't just depend on the size of electricity. Assuming that the heat loss and other energy losses are not taken into account, the heat required and the electric energy consumed for heating the same pot of water from 20℃ to 100℃ are the same, except that the heating time of 800 W is longer than that of1200 W. ........................., two points.

However, in fact, when the electric kettle is heated by an electric stove, it is also radiating heat. Because it takes longer to heat with 800W electric furnace, it will lose more heat, so heating to 100℃ needs more electric energy! Therefore, his idea is unreasonable. Therefore, it is more cost-effective to buy an electric furnace with higher electric power within the scope allowed by the user's watt-hour meter. Two o'clock in ..............................................

3.(4 points) Reference answer

Water vapor can only condense into small water droplets when it is cold to form "breathing" The measures taken by drivers are all based on the condition of inhibiting gas liquefaction ... 1 score.

In winter, drivers use warm air to raise the temperature of the windshield, so that water vapor cannot liquefy on the windshield and form "breath" ... 1 min.

It rains heavily in summer and the temperature outside the car is low. After closing the window, the temperature inside the car is high and the temperature of the windshield is low. When the water vapor in the car is left out on the windshield, it can condense to form a "breath". At this time, the air conditioner is turned on for refrigeration, so that the temperature in the car is lower than the temperature of the windshield, and the water vapor in the car cannot be liquefied on the windshield, thus preventing the generation of "breath". .......................................................................................................................................

4.(4 points) Reference answer

(1) Other things being equal, the larger the pipe diameter, the more difficult it is to generate bubbles. The ................. score is 1.

(2) the type of liquid, the concentration of liquid (or the temperature of liquid, the amount of liquid immersed, the strength of blowing bubbles)

................................................. 1.

(3) Design scheme based on liquid concentration: 2 points for ...............................

(1) Add different amounts of washing powder into two cups with the same amount of water and mix them evenly;

(2) Immerse the test tube into one of the cups, and blow hard to observe the bubble generation;

③ Dip the same amount of liquid in another cup with the same tube and blow with the same force to observe the generation of bubbles.

5.(4 points). Reference answer.

(1) Expand the heat dissipation area (or contact area with air) ................................. 1.

(2) For the same liquid in the communication device, the liquid level at rest is flat ........... 1.

(3) The pipeline along the vertical direction is convenient for the heat transfer oil in the transformer to form convection and enhance the heat dissipation capacity. .................: 1.

(4) If the heat transfer oil in the transformer oil tank is full, the heat transfer oil will burst the transformer and cause an accident. .................................................. 1.

Four. (8 points) Reference solution:

If the circuit is connected correctly, the circuit can be calculated. When the contact P slides to the A terminal, the electric blanket is directly connected to the power supply, and the voltage Ux at both ends of the electric blanket is the voltage at both ends of the power supply, that is, UX = 6V；; When the contact P slides to the terminal B, the electric blanket is connected in series with R, and then the power supply is connected. Two points will be deducted at both ends of the ........... power supply where the electric blanket and R*** share the voltage.

At this time, if Rx > > r, the voltage Ux across the electric blanket is much greater than the voltage UR across the sliding rheostat, that is, Ux ≈ u. Therefore, no matter how to adjust the position of the contact P, the voltage UX across the Rx will hardly change. It can be seen that the voltage values at both ends of the electric blanket in Xiaoming's experiment cannot be effectively changed because the resistance of the electric blanket is much greater than the total resistance of the rheostat. ......................., two points.

Without changing the experimental equipment, the circuit can be connected into the structure shown in Figure L, that is, in the circuit shown in the original circuit diagram, a wire bc is connected from the B terminal of the sliding rheostat to the negative electrode of the power supply. In this way, when P slides to the A end, UX = 6V；; When P slides to terminal B, Rx is short-circuited by conductor bc, and UX = 0V. Therefore, the voltage value on Rx varies from 0V to 6V in a wide range, and the ................... is 4 minutes.

Verb (abbreviation of verb) (10 points) reference solution

1. Regardless of the internal resistance of the battery, when the light from A to R 1 is blocked, R 1 increases.

(1) Because I =, I decreases.

The voltage across R 1 is U 1 = u-IR2. Because I decreased, U 1 increased .............. by 3 points.

(2) the power consumed by the photoresistor R 1 is p 1 =, because u 1+(u-u 1) = u is a certain value.

Therefore, when U 1 = U-U 1, U 1 (U-U 1) is the largest and Pl is the largest. That is, when r 1 = R2, P 1 has a maximum value.

Therefore, when R 1 increases, the power P 1 consumed by R 1 decreases. ................................, 3 points.

2. t = = s = 50s, 2 points for .............................................

3. The average passenger flow is: k = × 20 %× 60s = 24 people/minute. .............................................................................................................................................

6. (10) Reference answer

1. A one-way valve should be added, and its position is shown in Figure 2: …4 points.

2. To jack up heavy objects, the work done by the big piston should be:

W big = GH = mgh = 300J ...............................................................................................................................................................

The work done by maintenance personnel should be: wf = = j = 375j ..................1min.

The average power consumed by maintenance personnel is: pf = = j/s = 6.25w...............1.

When the heavy object is lifted at a uniform speed, the supporting force f of the big piston to the heavy object is large = mg = 1.0× 104N. ....................................................................................................................

Because the area s of the large piston is large = 8s is small, the force acting on the small piston

F small = F big =×1.0×104n =1250n ...........................................................................1min.

Because OA= OB on the lever, the mechanical efficiency eta of the hydraulic jack = 0.8,

Therefore, the force FB applied by the maintenance personnel to the B end should be: FB = = n = 3 12.5 n … l minutes.

Seven, (13 points) reference solution.

1. Figure 3 shows the circuit diagram of power supply and consumption. ...................., 3 points.

2. When both households use electricity, the total current in the line is the largest.

I always = = = 36.4a

Look-up table shows that ............................................................, a copper-core rubber insulated wire with a cross-sectional area of 4mm2, should be selected for 3 points.

3. The resistance of each 50m-long copper conductor is r = 4.25× l0-3× 50 = 0.2 1 (ω). .........................................................................................................................

The total equivalent resistance of each consumer appliance is r a = r b = =12. L (ω)... 1.

The total equivalent resistance of the whole hospital is r = 2 r+= 6.3 (ω).

The main current is I, totaling' = = 34.9 (a) ................1min.

The voltage across user A is U A = U-I, totaling' r = 220-34.9× 0.21= 212 (v). .....................................................................................................

The voltage across user b is U B = R B =× 12. L = 208 (V) ...................................................................................................................................

The power consumed by user B is Pb = = 3.58×103 (w) ....................1min.

Other solutions, as long as they are correct, will be graded with reference to the above grading standards.

Eight, (14 points) reference answer

1. When the power supply voltage is 36V and the current is 10A, the power supply can be L H. ....................................................................................................................................

2. Because the electric bicycle runs at a constant speed, the traction and resistance provided by the engine are equal:

F = f = 0.02× (m1+m2) g = 0.02× (70kg+40kg )×10n/kg = 22n ....................1min.

Within 20 minutes, the distance traveled by the bicycle is s = v t = 6m/s× 20× 60s = 7200m ...1.

Work done by motor on bicycle w = fs = 22n× 7200m = l.584x105j ...............1.

The total work done by current is W = = J = 1.98× 105J. .............................................................................................................................................

The current through the coil I = = = 4.58a .............................1min.

3. The power consumption cost of electric bicycle per 100km is 2×0.6kW? H×0.5 yuan /kw? H = 0.6 yuan ... l points.

The fuel consumption of motorcycle 100km is 2.5L×5. 1 yuan /l = 12.75 yuan. .........................................................................................................................

It can be seen that the cost of electric bicycles per 100km is much lower than that of motorcycles. So it is more economical to use electric bicycles. ..................................................................................................................................................................................

4. Motorcycles will emit exhaust gas when working, which will produce noise and cause great pollution to the environment. ............................................ got an l.

Although electric bicycles do not emit exhaust gas and have no noise when working, most electric bicycles on the market now use lead-acid batteries, which need to be replaced after about one year. The lead and acidic substances spilled from the corroded battery are very harmful to soil and human health. Lead is a kind of heavy metal with neurotoxicity, which will cause damage to human brain, resulting in low central nervous system function and abnormal neurological and behavioral functions. ..... l points

5. The passenger transport efficiency of electric bicycle and automobile is expressed by η 1 and η2 respectively, then

= = 24: l .............................................................. 2 points.