![](data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 72 71" width="72"></svg>)
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
Let the initial velocity of the last 200m fall be V, and take g = 10m / S ^ 2, then the formula is as follows:
vt+0.5gt^2=S
4v+0.5*10*4*4=200
v=30m/s
The total falling time can be calculated:
T=t1+t2
T=v/g+t2
T=30/10+4=7s
Calculate the total height:
H=0.5gT^2
H=0.5*10*7*7=245m
For free falling objects, the ratio of time taken to fall to the same height from the starting point is () The answer is (root 2 + 1): 1
First H = 1 / 2gt1 ^ 2 T1 = root (2H / g)
Second H = VT + 1 / 2GT ^ 2 v = GT1 = root (2GH)
T = 2 + 1 times root (2H / g)
A small ball, free fall Finally, he will move in a straight line at a uniform speed, and the acceleration is 0 Gravity is now equal to air resistance If gravity does not change, it can be seen that the air resistance is increasing all the time Why does the air resistance increase in the process of free fall?
When the free falling body moves, the falling speed of the object is directly proportional to time, and the air resistance is directly proportional to the third power of the speed. Therefore, the air resistance of the free falling body becomes larger and larger until the deceleration generated by the resistance and the gravitational acceleration balance. At this time, the free falling body maintains a constant speed, and the air resistance is a constant. However, because the resistance coefficient between the object and the air is very small, In the earth's gravity field, the latter cannot happen
Is it true that a particle is an idealized model and has no practical significance
A particle is an idealized model
Meaningless, wrong
When the shape and size of an object have little effect on the problem we study, we can regard the object as a particle
"Particle is an idealized model, which has no practical significance." why is this sentence wrong?
Particle is an idealized model, but it has practical significance. Although it is simulated and does not exist, it is convenient for us to study the influence of this material that can ignore mass and volume on other objects!
"Particle" in physics is an idealized model. When studying the motion of the following objects, it can be regarded as a particle () A. To study the over stroke movement of athletes in high jump B. Study the rotation of the earth C. Calculate the ship's speed in the ocean D. Study the receiving and serving technology of table tennis
A. The study of athletes' pole crossing action in high jump can not be regarded as a particle, otherwise it will be impossible to study the action. So a is wrong
B. When studying the rotation of the earth, it can not be regarded as a particle
C. When calculating the speed of a ship in the ocean, it can be regarded as a particle, so C is correct
D. When studying the receiving and serving technique of table tennis, we can't regard it as a particle, otherwise there will be no rotation, so D is wrong
Therefore: C
RELATED INFORMATIONS
- 1. 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
- 2. 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
- 3. 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
- 4. 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?
- 5. 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
- 6. On December 26, 2004, a century tsunami occurred, but animals did not die on a large scale. From a physical point of view: () A some animals can hear ultrasonic waves B some animals can hear infrasound waves
- 7. Hawking introduction
- 8. What is the reason why China's legitimate seat in the United Nations has been restored and China US relations have begun to normalize? A successful development of atomic bomb B improvement of China's comprehensive national strength
- 9. What is the noun interpretation of law?
- 10. How to understand the true meaning and revolutionary nature of Hegel's philosophy and the internal contradiction of Hegel's philosophy?
- 11. 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
- 12. The derivation of the relationship between velocity and displacement in free fall motion
- 13. 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
- 14. 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
- 15. 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 __
- 16. 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,
- 17. 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
- 18. 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
- 19. 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
- 20. 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?