1. A solid ball is placed into two containers containing enough water and enough alcohol. The forces on the ball are 0.9 N and 0.8 N respectively. The force of the alcohol is 0.8 ×103 kg/m3.
1. Analyze the floating and sinking state of the ball in water and alcohol
2. Find the density of the small ball
Solution: Assuming that the small ball does not float in water or in alcohol, or is suspended or floated and suspended, then it should be:
Because the question has been solved The known conditions are contradictory, so it is impossible;
Assuming that the ball sinks to the bottom in both water and alcohol, it should be:
Because it is contradictory to the known conditions of the question, so it is also impossible.
From the above analysis, it can be seen that when the ball is in water or alcohol, it can only float and sink.
And because of , the ball must float in water and sink to the bottom in alcohol.
(2) Since the ball floats in the water,
∴ ①
From the known conditions:
Obtain ②
Substitute formula ② into formula ① to get:
Figure 1
2. A cube wooden block with a volume of 1.0×10-3m3 is put into the equipment as shown in Figure 1. In a water container, the height above the water surface after being stationary is 5×10-2 meters, and the bottom area of ??the container is 0.04m2 (g is 10N/kg).
Find: ① the buoyancy force on the wooden block;
② the gravity of the wooden block;
③ the pressure increased at the bottom of the container after the wooden block is put in
④If this wooden block is put into a certain liquid, the height of the exposed liquid surface is 4 cm, find the density of the liquid.
Solution: ①5N; ②5N; ③125Pa; ④0.83×103kg/m3
Figure 2
3. For the circuit shown in Figure 2, the power supply voltage is not change, the resistance of R1 is 10 ohms, close the switch S, the slide of the sliding rheostat slides to point b, the ratio of the voltmeter and the indication is 5:7, the sum of the power consumed by R2 and R is the power consumed by R1 4 times, find:
①The ratio of the current passing through R1 and R2
②The maximum resistance of the sliding varistor Rab
③The sliding blade of the sliding varistor is in a , the power consumption ratio of R1 at two points b
Solution: ①1:1; ②25 ohms; ③4:1
Figure 3
IV. Figure 3 As shown in the figure, an object A weighing 600N is pulled by a pulley block to move at a constant speed in the horizontal direction. The object moves 8 meters in 40 seconds, and the work done by relay F is 1280 J. Find:
①The magnitude of the pulling force F and the power of the pulling force
②If the weight of the moving pulley is 12 N (excluding rope weight and friction), calculate the mechanical efficiency of the pulley block
< p>Solution: ①80N, 32w; ②92.5%Figure 4
5. In the circuit shown in Figure 4, R1 and R2 are fixed value resistors, and the lamp L Marked "16V4W", the supply voltage remains the same.
①Close the switches S, S1, and S2. The ammeter indicates 0.35 A. At this time, the lamp L can emit light normally. Find the size of the resistor R1;
②Close the switch. S, turn off switches S1 and S2, and the voltmeter's indication changes by 3.2 volts compared with ①. Find the electrical power consumed by resistor R2 at this time (the filament resistance remains unchanged)
Solution: ①160 ohms; ②0. 64w;
Figure 5
6. In the circuit shown in Figure 5, the power supply voltage remains unchanged and the switch S is closed. It is known that when the slider P slides to terminals a and At terminal b, the ratio of electrical power consumed by resistor R1 is P1:P2=9:4.
When the slider is at terminal a, the ammeter indicates 3 amps. When the slider P is at terminal b, the voltmeter indicates 6 volts. Find:
①The resistance and sliding value of resistor R1 The maximum resistance value of the rheostat R2
②What is the power supply voltage in volts
Solution: ①R1=6 ohms, R2=3 ohms; ②18V;
Figure 6< /p>
7. In the circuit shown in Figure 6, R1=400 ohms, R3=20 ohms, and the power supply voltage U=12 volts remains unchanged. When S1 and S2 are disconnected, the ammeter indicates The number is 0.1 ampere. Find:
①The resistance of R2
②The indication of the ammeter when S1 and S2 are closed
③When S1 and S2 are closed, it can charge 10 seconds of heat generated by the circuit.
Solution: ①100 ohms; ②0.15A; ③18 joules;
Figure 7
8. Connect a small light bulb with a rated current of 0.2 A The input voltage is always 9 volts at both ends of the power supply. For safety reasons, a small light bulb is connected in series with a sliding rheostat and then connected to the circuit, as shown in Figure 7. After the switch is closed, the slider is moved. When the sliding rheostat consumes 1.04 Watt hour, the small bulb happens to glow normally.
①What are the rated voltage and rated power of the small light bulb?
②When the small bulb emits light normally, what is the resistance of the varistor connected to the circuit?
③Move the varistor slide, and when the current in the circuit is 0.1 A, the actual power of the small bulb How much is it (not counting the effect of temperature on the filament cathode)
Solution: ①3.8V, 0.76W; ②26 ohms; ③0.19W
Figure 8
9. As shown in Figure 8, the resistance of R1 is 20 ohms. After the switch S is closed, the reading of ammeter A is 2.7 amps, and the reading of ammeter A1 is 1.8 amps. Find:
①The power supply Voltage
②The resistance of the electric meter R2
③The work done by the current passing through the resistor R2 per minute
④The ratio of the electrical power of the resistors R1 and R2
p>
Solution: ①36V; ②40 ohms; ③1944 joules; ④2:1
Figure 9
10. For the circuit shown in Figure 9, the power supply voltage remains unchanged and closed Switch S, when the slider P of the rheostat is at the midpoint a, the voltmeter reads 3 volts and the ammeter reads 0.6 amps; when the slider P is at end b, the voltmeter reads 5 volts and the ammeter reads 0.5 amps. Please calculate 5 physical quantities related to the circuit based on the measured data.
Solution: At point a, ①R2= U1/I1=5 ohms; ②P2=U1I1=1.8W; ③R2= U2/I2=10 ohms; ④P2=U2I2=2.5W. At point a, U =I1R1+U1, at point b, U=I2R2+U2
Figure 10
11. As shown in Figure 10, the cube wooden block floats on the water, with total 1/5 of the volume is above the water, and the inextensible suspension line is in a relaxed state. It is known that the maximum pulling force that the rope may bear is 5N, the side length of the wooden block is 0.1 m, the bottom area of ??the container is 0.03 m2, and there is a valve K at the bottom of the container , find:
①The density of the wooden block;
②Open the valve to let the water flow out slowly. When the string breaks, close the valve. At this time, the volume of water displaced by the wooden block is How many?
③After the rope is broken, when the wooden block floats again, how does the pressure of the water at the bottom of the container change compared to the moment when the rope is broken? How does the pressure of the water at the bottom of the window change? How much has changed? (g is 10 N/kg, hint: the two interacting forces are always of equal magnitude)
Solution: ①0.8×103kg/m3; ②3×10-4m3; ③The pressure of water changes Larger, △P=ρwater g△h=250Pa
Figure 11
12. In the circuit diagram shown in Figure 11, the small light bulb L is marked "8V 3.2W ", the maximum value of the sliding rheostat is 40 ohms, and the resistance of R1 is 18 ohms. Find:
①The resistance of the small light bulb L
②When S, S1, and S2 are all closed , the reading of the voltmeter is 9 volts, find the power supply voltage and the electric power consumed in the resistor R1
③Open S1 and S2, close S, if the range of the voltmeter connected to the circuit is changed to 0 -3 volts. The measuring range of the ammeter is 0-0.6 A. In order to ensure that neither meter exceeds the measuring range and that the voltage at both ends of the small bulb does not exceed its rated voltage, what is the range of resistance change of the sliding rheostat?
Solution: ①20 ohms; ②9V, 4.5w; ③2.5 ohms~10 ohms
Junior high school physics senior high school entrance examination final question training
One mechanics comprehensive question
p>
1 (2007 Suqian City) As shown in the figure, an object with a mass of 60 kg and a base area of ??0.1m2 makes uniform linear motion under the action of a pulley set of 25N. The sliding friction force on the object is known Find the following for 0.1 times the weight of the object:
(1) Draw a schematic diagram of the pressure of the object on the horizontal ground on the graph
(2) What is the gravity exerted by the object?
(3) What is the pressure the object exerts on the horizontal ground when it is at rest?
(4) What is the mechanical efficiency of this pulley block?
2. (2007 Maoming City) A large wooden box with a bottom area of ??0.4m2 was originally placed on the level ground. Now someone uses a trolley to push it from the bottom of the slope to the top of the slope at a constant speed. The whole process takes 10 seconds. , it is known that the wooden box weighs 400N, the person weighs 600N, the pushing force of the person on the wooden box is 75N, the length of the inclined plane is 4m, and the height of the inclined plane is 0.5m. Find:
(1) The force of the wooden box on the horizontal ground Pressure (2) The speed of the wooden box upwards along the incline
(3) The useful work done by people on the wooden box (4) Mechanical efficiency in this case
3. (2007 Liaocheng) An apartment building is 40m high. To complete the building, 10 4m3 of reinforced concrete and 3.5×104t of other building materials are required to complete the building. (The density of concrete is known to be 2.5×103kg/m3)
(1 ) To provide tap water from the ground to the roof, what is the minimum pressure that the pressurizing equipment needs to exert on the water?
(2) If 120m3 of water is sent from the ground to the roof every day, how much work must be done on the water every day?
(3) Measurements show that the pressure endured by the foundation of the building shall not exceed 1.2×106pa. If the contact area between the foundation and the ground is 1×103m2, then the additional decorative materials added to the building will be How much must the total mass of equipment, other materials, and people entering and exiting the building exceed?
Cylinder immersion depth h (cm) 0 0.6 1.2 1.8 2.4 3.0 3.6 4.2 4.8 6
Dynometer indication F (N) 3 2.85 2.70 2.55 2.4 2.4 2.4 2.4 2.4 2.4
4. (2007
Meizhou City) There is a spring dynamometer hanging from a solid cylinder. When the cylinder is gradually immersed in a cylindrical beaker filled with water (as shown in the figure), observe the changes in the spring dynamometer's indication as shown in the table below. Demonstration test: According to the conditions given in the table, find:
(1) The pressure at the bottom of the cylinder when the depth is 0.3m
(2) The mass of the cylinder< /p>
(3) Density of cylinder
Self-weight 15t
Load capacity 20t
Number of car wheels 10
The contact area between each tire and the ground is 0.05m2
5. (2007 Hebei Province) Cars are a familiar means of transportation. In order to reduce operating costs, some units wantonly overload, causing damage to the road surface. Some parameters of a certain type of transport vehicle are as follows. Please ask: (1) If there is 12m3 of sand in the compartment of this vehicle, please answer through calculation. Is the vehicle overloaded? How much pressure does the car exert on the horizontal road at this time? (ρsand =2.5×1.03kg/m3) (2) It is known that the distance from the sand field to the construction site is 180km. When the vehicle is fully loaded and runs normally with a power of 140kw, can it go from the sand field to the construction site within 2 hours? (The resistance the car experiences is 0.02 times the weight of the car)
Electricity Comprehensive Questions
6. (2007 Ningbo City) A student used the circuit in Figure A to conduct the following research on a small light bulb with a fuzzy rated voltage and a rated power of 1w. After connecting the circuit as shown in A, close the switch S and measure the current through the small light bulb and the small light bulb. The voltage relationship at both ends is shown in Figure B.
(1) Judging from the picture, the resistance of the small light bulb during the experiment is (optional "constant" or "changing").
(2) When the voltage across the small bulb is 0.5V, how much power does the small bulb consume in 2 minutes?
(3) What is the rated voltage of the small light bulb?
7. (2007 Yangzhou City) In the circuit in Figure A, the power supply voltage is 9V and remains unchanged, the ammeter specifications are 0~0.6A, the voltmeter specifications are 0~15V, and the voltage on the light bulb Marked with the words "6V 6W", the relationship between the bulb current and the voltage change is shown in Figure B. Find:
(1) The current when the bulb lights normally
(2) When the current When the indicated number is 0.4A, the indicated number of the voltmeter
(3) In order to ensure the safety of the circuit, the minimum resistance value of the sliding rheostat in the circuit and the consumption of the circuit at this time total power.
8. (2007 Chengdu City) As shown in the figure, a light bulb L marked with "8V 4W" is connected in series with a sliding rheostat R. The switch S is closed and the slider P is at terminal b. The voltmeter shows 12V and the bulb lights normally. When the slider slides from point b to point a, the resistance in the circuit increases by 6Ω. Find: (1) The resistance value and power supply voltage of the light bulb (2) When the slider P is at point a, what is the actual power of the light bulb?
(3) What approximations did you use in the calculation process?
9. (2007 Weihai City) As shown in the figure, the power supply voltage is constant 24V, the small light bulb is marked with "6V 3W", the resistance of the fixed value resistor R2 is 24Ω, when the switch S is closed, When S1 and S2 are both disconnected and the slider moves to the midpoint of the sliding rheostat, the lamp L lights normally
(1) What is the resistance of the bulb L?
(2) What is the maximum resistance value of the sliding rheostat?
(3) When S1 and S2 are both closed, adjust the sliding rheostat to minimize the power consumed by the entire circuit.
What is this minimum value?
Electricity and Mechanics Comprehensive Questions
10. (2007 Putian City) Xiaoqiang used the physics knowledge he learned to design a tension gauge. Picture A is its schematic diagram. The right end of the hard spring It is fixed with the metal slider P (the resistance of the spring is not counted, and the friction between P and R1 is not counted). The fixed value resistance R0=5Ω, a b is a uniform resistance wire 5 cm long, its resistance value is 25Ω, the power supply voltage U=3V, the range of the ammeter is 0~0.6A, please answer:
(1) Xiaoqiang’s purpose of connecting R0 in the circuit is.
(2) When the pull ring is not stressed, what is the reading of the ammeter after the switch S is closed between the slide plate and terminal a?
(3) It is known that the relationship between the extension length ΔL of the spring and the tensile force F is shown in Figure B. Through calculation, it is shown that after the switch S is closed, when the ammeter pointer points to 0.3 At position A, what is the horizontal rightward pulling force acting on the pull ring?
11. (2007 Huangshi City) As shown in the picture is a schematic diagram of the electronic scale designed by Xiaoxing using the physics knowledge he learned. The tray, the upper end of the spring and the metal slide P are fixed together, and the fixed value resistor R0 =5Ω, ab is a uniform resistance wire with a length of 5cm, the resistance R=20Ω, the power supply voltage U=3V, the range of the ammeter is 0~0.6A, (the resistance of the spring is not included, and the friction between P and R is not included) Find:
(1) When there is no object in the tray, let the metal slide P be at the uppermost end of R. After closing the switch, what is the reading of the ammeter?
(2) It is known that the relationship between the compressed length ΔL of the spring and the pressure F is as shown in the table below. After the switch S is closed, when the ammeter pointer points to 0.2A
What is the mass of the object in the tray?
12. (2007 Meizhou City) As shown in the figure, it is a schematic diagram of an electronic scale made by a research and study group. It uses a voltmeter to indicate the mass of an object. The pallet, the upper end of the spring and the sliding The rheostat slides are fixed together. The mass of the tray and spring is not counted. There is a retractable wire between OA. When there is no object in the tray, the voltmeter indicates 0. It is known that the resistance R0=5Ω, the maximum resistance of the sliding rheostat is 15Ω, the power supply voltage U=3V, and the range of the voltmeter is 0~3V. Now place a 1kg object in the tray, and the slider is just 1/3 away from the upper end of R (disregarding friction, the spring is always within the elastic limit), please calculate the answer:
(1) When a 1 kg object is placed in the tray, what is the reading on the voltmeter?
(2) What is the maximum mass that this electronic scale can measure? How many volts should this mass number be marked on the voltmeter?
13. (2007 Lishui City) Xiaowen designed a pallet scale for measuring the gravity of objects. The picture is a schematic diagram of the principle. The pallet is used to place the measured object. The OBA can rotate around the 0 point. lever, R1 is a pressure sensor, (its resistance value will change with the change of the pressure, the change relationship is as follows), R0 is a fixed value resistor, which is an instrument that displays the gravity (essentially a measuring range of 0~3V Voltmeter), it is known that OA:OB=2:1, R0=100Ω, the power supply voltage is always 3V (ignoring the gravity of the tray, lever and pressure bar)
(1) When there is no object on the tray , the resistance value of pressure sensor R1
(2) When the object to be measured is placed on the pallet, the voltmeter indicates as shown in the figure, what is the voltage on pressure sensor R1 at this time?
(3) What is the gravity of the object measured in question (2)?
14 (2007 Nanjing) A research study group designed a device to measure wind force. The principle is as shown in the figure. The windward plate is connected to one end of a lightweight spring and worn on a smooth metal rod. , the spring is made of insulating material, and the resistance of the uniform metal rod changes uniformly with the length. When working, the windward plate is always facing the direction of the wind. In the circuit, the left end wire is connected to the M end of the metal rod, and the right end wire is connected to the N point on the windward plate and can slide on the metal rod with the windward plate. The wires at both ends are in good contact with the metal rod. It is known that the power supply voltage is constant 4.5V, the planting resistance R=1.0Ω, the relationship between Rx when the metal pole is connected to the circuit and the wind force F endured by the windward plate is as shown in B,
(1) If the circuit Connect a voltmeter to the instrument so that the voltage indication increases with the increase in wind force. Please draw the voltmeter at the appropriate location.
(2) When there is no wind, find the indication of the voltmeter and the electric power consumed by the fixed value resistor R;
(3) If the range of the voltmeter is 0~3V, find The maximum wind force that the device can measure
Comprehensive questions on electricity and heat
15. (2007 Guiyang City) In an extracurricular activity, Xiaoyue made relevant observations on household induction cookers and research, and recorded the relevant data of the induction cooker and her household electrical energy meter, as shown in the table below: Please use the relevant information obtained by Xiaoyue during the activity to borrow the objects to observe during this period
Record research activities
The nameplate of the induction cooker U amount = 220V P amount = 1kw ① Use the induction cooker to heat a pot of water (the mass of the water is 2kg, and the initial temperature is 30℃. ② Turn off other electrical appliances at home, only Connect the induction cooker to the circuit to boil water, and observe that the electric energy meter dial rotates 150r within 5 minutes. At this time, the temperature of the water measured with a thermometer is 50℃
The nameplate of the electric energy meter is 220V 10 (40) A< /p>
50HZ 2000r/kwh
(1) The heat absorbed by the water (2) The actual power of the induction cooker (3) The efficiency of the induction cooker in boiling water
16.( 2007 Weihai City) Classmate Xiaogang’s family bought a new electric water heater. Some of the data on the nameplate are shown in the table below
(1) What is the current and resistance of the water heater when it is working normally
Model PCD-H40II
Volume 40L
Rated maximum temperature 75℃
Rated voltage 220V
Rated power 1.1KW
Rated internal pressure 0.75MPa
(2) If the actual voltage on the circuit is only 200V during the peak period of electricity consumption, it will take 38.5 minutes for the water heater to heat 20kg of water from 20℃ to 40℃. What is the heating efficiency of the water heater during this time (not considering the change of resistance with temperature)
Rated voltage 220V Function Steam ironing and dry ironing
Rated frequency 50HZ Steam method dripping type
Rated power 1000W Mass 1.3kg
Bottom area 160cm2 Placement method Self-standing
17. (2007 Zhenjiang City) As shown in the picture, it is a household steam electric iron Actual picture and nameplate. During use, water in the water tank drips into the heated soleplate steam chamber and vaporizes rapidly to generate downward steam
(1) Inject 0.3kg of water into the iron water tank.
Put it flat on a horizontal table.
Find: the pressure of the iron on the clothes
(2) Preheat the iron before steaming it so that the temperature of the metal base plate When the temperature rises from 20℃ to 220℃, the temperature control switch automatically turns off. It is known that the mass of the metal is 1kg and the specific heat capacity of the metal base plate is 0.46×103J/(kg℃). How to preheat a steam iron How much heat does the metal base absorb during the process?
(3) During steam ironing, water drops into the steam chamber and takes away heat as the water heats up and vaporizes. When the temperature of the metal base plate drops to 190°C, the temperature control switch automatically closes and the iron works normally. When heated to 220°C, the temperature control switch automatically turns off and stops heating, and so on. If the working conditions of the steam iron change as shown in the figure, how much electricity will be consumed to iron a piece of clothing in 12 minutes?
18. (2007 Suifang City) Xiaoxing designed an automatic control device for his own electric bathing water heater. As shown in the figure, R1 is a thermistor (placed in the water heater), and its resistance The relationship between the value and temperature is shown in Table 1. Table 2 is the nameplate of this electric water heater. It is known that the relay coil resistance R2 is 10Ω, and the voltage U0 of the left power supply is 6V unchanged.
When the current in the relay coil R2 increases to a certain value, the armature of the relay is sucked down, the circuit of the electric water heater is closed, and it starts to work. Please answer
(1) During normal operation, the resistance of the electric water heater How much?
(2) Analyze Table 1, how does the resistance of the thermistor change with temperature?
(3) If the temperature inside the electric water heater is controlled between 30℃ and 60℃, what is the operating current of the relay coil when the armature is sucked down and the circuit of the electric water heater is disconnected?
(4) When the electric water heater is working normally, how long does it take to heat the entire tank of water from 30℃ to 60℃? (Excluding heat loss)
19. (2007 Linxi City) The data of Huayang 1870 series solar water heaters are as follows:
Evacuated tube diameter (mm) 70×1800 Specifications (branch pipe) 15
Outline dimensions (mm) 1840×1597×1765 Thermal insulation layer (mm) 60
Water tank capacity (L) 150 Lighting area (m2) 2.1
( 1) It is known that the average solar radiation energy received per square meter in our city facing the sun in one hour is 3×106J. If the time of receiving solar energy is calculated as 8 hours a day, the water heater can convert 50% of the received solar energy into the internal energy of water. Under normal circumstances, the water heater can How many degrees Celsius can a box of water with an initial temperature of 20℃ be heated to?
(2) If an electric water heater marked "220V 1500W" is used to operate at the rated voltage, how long will it take to raise the same box of water to the same temperature?
(3) If the electricity price is 0.54 yuan/KWh. Based on this calculation, how much electricity can be saved per month (based on 30 days)?
20. (2007 Xiamen City) There is an automatic electric heating bottle in the office. The picture and table show its principle and parameters.
A is an automatic temperature control switch, which automatically disconnects the circuit when the water temperature reaches the set temperature;
automatically connects the circuit when it is lower than the set temperature. It is known that the specific heat capacity of water is
4.2×103J/(kg?℃). Please make the following calculations through analysis:
(1) 90% of the heat released by the electric hot water bottle is This water absorbs and boils a bottle of water at 20℃ (standard atmospheric pressure). How long should the electric hot water bottle work normally?
(2) When the yellow light is on, is the electric hot water bottle in a heat preservation state or a heating state? What is the resistance of the thermal insulation element
R when it is working? (Note: The power consumed by the indicator light can be ignored, and the heat preservation power
refers to the power consumed by the entire circuit)
Model P2155-B
Power supply AD220V 50HZ
Heating power 800W
Insulation power 40W
Capacity 2.0L
Fuel gasoline
Fuel tank volume 50L< /p>
Gasoline density kg/m3 0.7×103
Gasoline calorific value J/kg 4.6×107
Produced by complete combustion of fuel
The percentage of heat converted into
mechanical energy is 40%
Comprehensive questions on mechanics and heat
21. A car drove at a constant speed of 70km on a straight road. The speed of the car was 72km/h and the maximum consumption of gasoline was 6L. Please follow the relevant information provided in the table below.
For information, calculate how many kilowatts the car uses when driving.
Moped 93# gasoline
Fuel gasoline Density 0.7×103 kg/m3
Fuel tank capacity 7L Calorific value 4.6×107J/kg
Power 6KW Price 4.70 yuan/L
22. (20007 Taiyuan) Teacher Wang’s home is about 9km away from the school. In order to facilitate commuting, he bought a moped. The fuel used For 93# gasoline. The relevant parameters are as shown in the table. The calorific value of gasoline indicates that the heat released by complete combustion of each kilogram of gasoline is 4.6×107J.
If Teacher Wang’s average speed when riding a bicycle is 36km/h, please calculate the approximate time it takes for him to go from home to school (excluding energy loss)
(1) Approximate time;
(2) Motorcycle The quality of gasoline the car needs to consume;
(3) Fuel cost
Average speed 90km/h
Constant speed oyster sauce 9L/100km
Oil price 4.80 yuan/L
Gasoline density 0.75×103 kg/m3
23. (2006 Shenyang) On Sunday, my father drove Xiaomori to the Book City to buy popular science books. After returning, Xiaomori asked his father some questions about the car and made notes, as shown in the table below. Please calculate based on what Komori recorded:
(1) If the one-way time for Komori to go to the Book City is 20 minutes, how many kilometers is the distance between Komori's home and the Book City?
(2) How many kilograms of gasoline are used on the round trip? How much does it cost for gas?
24. A car is traveling at a constant speed of 1.8km on a straight highway. The speedometer of the car is as shown in the figure.
(1) What is the speed of the car? Kilometers per hour? How many meters per second?
(2) If the power of the car engine is 40kw, how much resistance will the car experience while driving?
(3) If a car consumes 0.25kg of gasoline, how efficient is its engine? (The calorific value of gasoline is
q=4.6×107 J/kg)
25. (2007 Baotou City) As shown in the figure is a circuit for automatically measuring the temperature and pressure in the pot Schematic diagram (the dotted box shows part of the circuit inside the pot). The power supply voltage is always 4.5V
(1) If a steel instrument with a total mass of 5Kg and an initial temperature of 15°C is to be sterilized, the sterilization temperature
must reach 115°C. How much heat does the device*** absorb? [C?Steel=0.46×103 J/(kg?℃)]
(2) The pressure sensor R1 (a variable resistor whose resistance changes with the amount of pressure it receives) is placed in the pot, < /p>
The pressure-bearing area is 2cm?2. If the maximum pressure that the surface of R1 can withstand is 70N, what is the maximum air pressure allowed in the pot
?
(3) A1 is an instrument (essentially an ammeter) that displays the air pressure in the pot. When the air pressure in the pot is not high
less than 1 standard atmosphere, A1 displays the air pressure value of 0. At this time, the resistance of R1 is 200Ω. Find: At what milliampere position should the zero scale of the barometer be marked on the dial of ammeter A1?
(4) The thermal sensor R2 (a variable resistor whose resistance changes with temperature) is placed in the pot, and A2 is an instrument that displays the temperature (essentially an ammeter); the relationship between the resistance of R2 and temperature As shown in the following table: When the ammeter A2 indicates 60mA, what is the temperature in the pot?
Temperature t/℃ 80 85 90 95 100 105 110 115……
Resistance R2/Ω 120 110 100 90 80 70 60 50……
Junior high school Review of physical calculations
1. Electrical calculations
1 There is a small light bulb with a rated voltage of 2.4V. The resistance of the small light bulb is 8Ω. If we only have a 3V power supply, we need to make the small light bulb For the light bulb to work properly, how large a resistor needs to be connected in series.
2. In the circuit shown in the figure, R2=20Ω, the total resistance in the circuit is 12Ω, and the ammeter indicates 0.3A. Please calculate
(1) The resistance of resistor R1 (30Ω)
p>
(2)Power supply voltage (6V)
(3)Current through R1 (0.2A)
3. As shown in the figure, "6V 3W" A small light bulb L is connected in series with a resistor with a rated power of 10W. The power supply voltage is 10V and remains unchanged. When the switch S is closed, the ammeter and voltage indications are 0.20A and 2.4V respectively. The resistance of the resistor and the small light bulb changes with temperature, regardless of the temperature. The change of . As shown in the figure, the power supply voltage is 6V, R1=R2=30Ω. Find
(1) When the switch is turned off, the total resistance in the circuit and the voltage across R2; (60Ω 3V)
(2) When the switch is closed, the ammeter indication and the voltage across R2. (0.2A 0)
5. In the circuit as shown in the figure, R1 is a sliding rheostat, R0 , R2 are both fixed-value resistors. The voltage at both ends of the power supply remains unchanged. Change the position of the slider of the sliding rheostat R1. The graphs of the changes in the indications of the two voltmeters with the current are drawn in the coordinate system shown in Figure B. , calculate the resistance value of R0 (2Ω) based on the above information
6. Xiao Ming uses the bulb L1 marked with "6V 6W" and the bulb L2 with "6V 3W" to conduct the experiment (1) When L1 glows normally When , what is the current through L1? (`1A) (2) As shown in Figure A: A and B are the curves of the relationship between the current through L1 and L2 and the voltage at both ends respectively. Now connect two lamps to the circuit as shown in Figure B, so that one of the bulbs can emit light normally. What is the total power consumed by the circuit? (4W)
7. When using an electric soldering iron to weld components, sometimes in order to save power and prevent the soldering iron tip from being too hot to be easily stained with tin, the circuit is controlled to have the following characteristics by controlling the switch: When not welding temporarily, the soldering iron It is in a heat preservation state and can reach the temperature quickly when welding is needed. It is known that the power supply voltage is 220V. The internal circuit diagram of the soldering iron is as shown in the figure. When the switch S is connected to a, the electric power P1 of the soldering iron is 100W. When the switch S is connected to b, The electric power of the soldering iron is P2. Question:
(1) When the soldering iron is in the heat preservation state, where is the switch connected? (point b)
(2) If P1=4P2 , what is the resistance of resistance wires R1 and R2? (484Ω 1452Ω)
8. After learning electrical knowledge, Xiaohong drew the circuit diagram of the hair dryer at home. She thought that when only switch S1 was closed, the hair dryer would blow cold air. When S1 and S2 were closed at the same time, The hair dryer blows hot air. Xiaofen looked at her circuit diagram and felt that there was a problem: if only S2 was closed, the heating wire R would work while the motor did not work, causing the plastic shell of the hair dryer to overheat and cause damage. Xiaofen thought that as long as the If one of the switches is moved to the dry road, the motor will be working when the heating wire R is working, thus ensuring that the plastic shell will not be damaged due to operating errors. Please analyze and answer the following questions:
( 1) Do you think Xiaofen should move the switch to the dry road to comply with safety requirements (S1)
(2) Based on the relevant data provided on the nameplate of the hair dryer, calculate when the hair dryer works normally and blows hot air When, how much electric energy is consumed in one minute? What is the electric power of the electric heating wire R? What is the current passing through the electric heating wire R?
(27600J 440W 2A)
9. A school sports ground is away from the The school's electrical control room is some distance away. An iodine tungsten lamp with a specification of "220V 1KW" is installed in the sports ground. It is known that the voltage of the electrical control room is constant at 220V. The distance between the electrical control room and the iodine tungsten lamp is 100m. The used The wire is a certain brand of copper core rubber insulated wire. The following table lists the safe current carrying capacity (that is, the maximum safe current when energized for a long time) of the brand's copper core rubber insulated wires with different cross-sectional areas at room temperature.
(1) The selected copper wire is required to comply with the principles of applicability and economy. Please explain through calculations which type of copper core conductor is used for the wire? (Looking up the table for 4.55A, we know that a copper core rubber insulated wire with a cross-sectional area of ??1mm2 should be used)
(2) If the resistance of the copper core wire used is 0.017Ω per meter, please use an iodine tungsten lamp When , how much electrical power is lost on the transmission line? (The total resistance in the circuit is 51.8Ω, the total current is 4.25A, and the power lost in the line is: 61.4W)
(3) How much power does the iodine tungsten lamp consume for one hour of lighting? (0.874KWh)
Conductor cross-sectional area S/mm2 0.5 1 1.5 2.5 4 6 10
Safe current carrying capacity I/A 4 8 12
20 25 32 50
10 As shown in the figure is a simple schematic diagram of an electric pressure cooker. A is the sealed pot body and the lid area is 400cm2.
R1 is the heating resistance during operation. L is the indicator light, its resistance is 20Ω, R2 is the insulation resistance, S1 is the power on
off, S2 is the pressure switch. After closing S1, the circuit heats the electric pressure cooker through R1. When the gas pressure in the pot
When the pressure reaches the set value, the water begins to boil, the bottom of the pot moves downward, the pressure switch is disconnected from contact point a, and connected to point
b to control the pressure. For the purpose of voltage and temperature control, the total power of the thermal insulation circuit is 20W.
Table 1 The relationship between the boiling point T of water and the gas pressure p
T/℃ 100.. 105 110 112. .114. 116. 118 120
p/kpa 101 121 143 154 163 175 187 199
Table 2 Nameplate of electric pressure cooker
Rated voltage Heating power Pressure setting value
220 V 1000W 175kpa
(1) When the pressure inside the pot is 121kp, what is the pressure of the gas in the pot on the lid? (4.84×103) (2) What is the resistance of the thermal insulation resistor R2? (2400Ω)
(3) It is known that the mass of the water in the pot is m, the initial temperature is T0, and the specific heat capacity is c. In order to find the efficiency of the voltage cooker from the beginning of heating to the time when the pot pressure reaches the set value , as long as the time t for the closed switch S1 to enter the circuit is measured, the expression of efficiency can be derived η= (expressed by a known quantity) [the indicator light is on; cm(116℃-T0)/1000W×t)]< /p>