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As shown in the figure, use the spring scale to horizontally pull the object block weighing 10N, place the object block on the horizontal desktop, and gradually increase the tension. When the indication of the spring scale is 2.2n, the object block begins to slide. In order to maintain the uniform movement of the object block, the later tension is only 2.0N. Then the maximum static friction between the object block and the desktop is______ N. The dynamic friction coefficient between the block and the table is __
(1) The wood block is still in equilibrium, and the friction force received by the wood block is equal to the horizontal tension of the spring dynamometer. When the wood block just starts sliding, the friction force is the maximum static friction force. According to the balance conditions, the maximum static friction force is Fmax = 2.2n. (2) the wood block moves at a uniform speed and is in equilibrium, which is obtained from the balance conditions
Physics problems come and help, it's easy! An individual weighs 49n and has a volume of 5 * 10 to the negative third power. When it is put into salt water, what is the buoyancy it receives at rest? When it is put into kerosene, what is the buoyancy it receives at rest? (the density of kerosene is 800kg / m3.) there should be a detailed answer process and explain why. Please!
1) 49n because of floating, the force is balanced
2) The negative third power of 5 * 10 * 800 * g = 40n didn't float this time and sank to the bottom
As shown in the figure, the length of the steel wire of the crane is L = 3M, and the hanging mass below is m = 2.8 × 103kg goods, traveling at a constant speed of V = 2m / s, suddenly braking, what is the tension on the steel wire rope?
After braking, the goods will move in a circle due to inertia. According to Newton's second law,
F-mg=mv2
L
The solution is f = Mg + MV2
L＝2.8 × 104+2.8 × one hundred and three × four
3N=3.173 × 104N
Answer: the tension of the steel wire rope is 3.173 × 104N．
The weight of Xiaoting's shoes for rope skipping is 0.4KG. She jumps 180 times in a minute. Assuming that the maximum height of her feet off the ground is 5cm each time, she will rise once. Does she work on the shoes (0.2j)? If the rise time takes 0.3 times of each jump time, what is the average power per rise? G takes 10N Also, I have an exam on Thursday
5cm = 0.05m 0.4KG = 4N w = 0.05 * 4 = 0.2j from w = f * s
Average time for one rise = 60 / 180 * 0.3 = 0.1s
From P = w / T, P = 0.2 / 0.1 = 2W
I hope it can be solved Here is an experimental plan for measuring the density of a non absorbent foam block using the "press in" method. A. Inject an appropriate amount of water into the measuring cylinder and read the water surface indication v1 B. light the foam block into the water and read out the number of V2. C. used balance to measure the quality of foam plastic blocks M D. uses small needles to press the foam blocks into the water just to immerse them. E. take out the foam block and measure its mass by balance M0 (1) You think the above experimental steps () are redundant, and the reasonable experimental order should be () (2) the density of foam plastic is P (this is meat) = (). Uh, missed one There is another sentence behind point D Read the water surface indication v3
B. E is redundant
Reasonable order C, a, D
m/(V3 - V1)
Or, in theory, a balance may not be used
Then C and E are redundant, and the order is a, B and D
ρ = ρ Water * (V2 - V1) / (V3 - V1)
However, this is the wrong experimental method, because the error of reading the scale of the measuring cylinder is much greater than that of the balance. Therefore, when both can be selected, the more accurate measurement method shall be adopted
Thank you first There is a mine with a depth of 100 meters and a ponding of 45 cubic decimeters per minute. In order not to leave water in the mine, at least what power pump should be used to pump water?
Ponding per second is 45 / 60, P = w / T, that is, P is equal to the work done by the water pump in one second
So p = 45 / 60 × one × g × one hundred
If G takes 10, P = 750W
RELATED INFORMATIONS
- 1. As shown in the figure, the parallel metal plates a and B placed along the horizontal direction are respectively connected with the positive and negative poles of the power supply. There is a small hole in the center of the two plates along the vertical direction. Now there is a positively charged droplet. The point P directly above the small hole falls freely from rest, and the speed after successively passing through the two small holes is V1. If the plate a does not move, if the key K is kept open or closed, B When the plate is translated upward or downward for a short distance, the same droplet still falls freely from rest at point P, and the velocity after passing through two small holes successively is v2. The following statement is correct without air resistance () A. If key K remains closed and plate B moves downward, V2 > v1 B. If key K is closed for a period of time and then disconnected, and plate B is moved downward, V2 > v1 C. If key K remains closed, V2 = V1 regardless of moving board B up or down D. If key K is closed for a period of time and then disconnected, no matter moving board B upward or downward, V2 < v1
- 2. Make up unit Zhang Wei's height is 16.6_____ 7.5km=______ m； 5.85mm=_____ m； 0.068m=_______ nm； 16.4m=______ um； 1.8h=____ min； 45min=_____ h
- 3. The derivation of the relationship between velocity and displacement in free fall motion
- 4. How to use the formula of uniform variable speed linear motion in senior high school physics compulsory 1 Is under what circumstances this formula is used
- 5. The time taken for an object to fall freely after the last 200 meters is 4 seconds, then what is the falling time and total height of the object
- 6. Particle is an idealized model. In the following examples, what can treat the research object as a particle is () A. Study the motion law of the earth around the sun B. Study the law of the alternation of day and night on the earth C. Study the time required for the train to run from Fuzhou to Shanghai D. Study the time required for a train to pass the Nanjing Yangtze River Bridge
- 7. A car traveling along a straight highway with uniform acceleration, passing two electric poles 50m apart by the roadside, shares 5S. When it passes the second electric pole, its speed is 15m / s, and when it passes the first electric pole, its speed is () A. 2m/s B. 10m/s C. 2.5m/s D. 5m/s
- 8. A physics problem about uniform variable speed linear motion in high school (about the proportional relationship in special laws) A train starts to move at a constant speed in a straight line from a standstill. One person stands in front of the first carriage to observe. The time for the first carriage to pass through him is 4 seconds, and the time for all trains to pass through him is 12 seconds. The distance between carriages is not recorded, and the length of each carriage is equal. It is required to (1) how many carriages in total; (2) How many cars passed this person in the last 4 seconds; How many seconds did the last three sections pass through this person? I hope it's best to use the proportional relationship in the special law, and attach the description and analysis, not just the formula and answer If the three questions are difficult to answer, you can answer the first one first
- 9. The object changes speed under the action of external force When an object changes speed under the action of external force, the kinetic energy must change The kinetic energy of an object remains unchanged, and the combined external force must be zero Why are these two sentences wrong?
- 10. The artificial satellite makes a uniform circular motion around the earth, its orbit radius is r, its linear velocity is V, and its period is t. if you want to change the period to 2T, what methods can be adopted: A. R remains unchanged, so that the linear velocity becomes 1 / 2V, B.V remains unchanged, and the orbit radius becomes 2R C. yes, the orbit radius becomes (3 times better, 4 times lower) d. increase the height of the satellite by R
- 11. The distance between the slide and the lens position changes between 15 ~ 30cm. In order to get an enlarged image on the screen, which of the following focal lengths should be selected () A. focal length 15cm B. focal length 30cm the correct answer to this question is a, but to get an enlarged image, the object distance should be between F < U < 2F. The farther the lens is, the larger the image will be. Why not choose B and a? Be clear,
- 12. When stone a falls freely from the top of the tower from static S1, stone B falls freely from static S2 from the top of the tower. If the two stones fall to the ground at the same time, the tower height is: () a S1 + S2 B (S1 + S2) ²/ 4S1 C S1 ²/ 4（S1+S2) D (S1+S2) ²/ S1-S2
- 13. As shown in Figure 1, the current in a long straight wire changes according to the sinusoidal law as shown in Figure 2. It is specified that the current is positive from left to right. There is an open metal frame below the straight wire. Therefore, compared with point B, the moment when the potential at point a is the highest is () A. T1 time B. T2 time C. T3 time D. T4 time
- 14. An object with a mass of M = 2kg is stationary on the horizontal plane, and the sliding friction force between the object and the horizontal plane is equal to 0.25 times of the elastic force between them. Now, apply an oblique upward pull force with a size of F = 8N and an angle of 37 degrees with the horizontal direction to the object. It is known that sin37 = 0.6, cos37 = 0.8, g = 10, and calculate the displacement through the object in 5 seconds under the action of the pull force
- 15. If a car flies on rainy days at a speed of more than 150 kilometers per hour, will part of the rain rub shoulders with the body because of the strong airflow formed by too fast speed? (provided that there is no rain from the start to the acceleration above 150, and the rain is not very heavy, between heavy rain and light rain) I just want to know whether an object will form a strong airflow around the body because of its too fast speed, and whether this strong airflow will change the orbit of the object to be contacted?
- 16. Moving car and laser beam That's it. I can't understand this question. I want to know how the laser beam moves? Is it a line or a face? Why are there two situations in the car? Where is the entry point?
- 17. As shown in the figure, when a charged body is contacted with a positively charged electroscope, if (1) The opening angle of the metal foil becomes larger, indicating that the charged body carries () charge (2) The opening angle of the metal foil decreases to 0 °, indicating that the charged body carries () charge (3) After the metal foil is closed and opened, it indicates that the charged body carries () charge, and the amount of charge is greater than that of the electroscope ()
- 18. If the threshed grains (such as wheat, rice, etc.) are mixed with a small amount of stems and leaves, shell debris or small sand particles, the grains can be lifted into the air with a lifting machine to separate the grains from the sundries, so as to obtain clean grains. The main reason why grains can be separated from other sundries is that they () A. The speed of being thrown into the air by the hoister is different B. Different density C. The gravity is different D. The air resistance after throwing is different
- 19. A junior high school physics problem about energy, who can solve it? A car's fuel tank was filled with 35kg gasoline. Xiao Wang drove to a place to perform a task, with a distance of 300km. When driving at a constant speed on the highway, the resistance of the car was 920n Note: 30% of the internal energy generated by complete combustion of gasoline is converted into mechanical energy; The calorific value of gasoline is 4.6 * 10 to the seventh power of joules per kilogram Q: (1) the work done by the traction force when the car reaches the destination; (2) The calculation shows whether the car needs refueling during driving Thank you!
- 20. According to the redshift phenomenon of the star spectrum, scientists infer that the universe is expanding and the planet is getting farther and farther away from us. In fact, there is a similar phenomenon in the sound in daily life. At the moment when the train sped past us, although the frequency of the whistle emitted by the train is constant, the tone of the sound we hear is different______ (select "from high to low" or "from low to high")