Factorization: 6 (a + b) ^ 2 + 40 (a + b) (a-b) + 25 (a-b) ^ 2

Factorization: 6 (a + b) ^ 2 + 40 (a + b) (a-b) + 25 (a-b) ^ 2

How is the distance between the earth and the sun calculated

Calculation with the formula of universal gravitation and centripetal force
G gravitational constant M solar mass m earth mass r sun earth distance t earth revolution period
GMm/r^2 =m(2π/T)^2 r
r^3=GM T^2 /(4π^2)

Exercises on the generation and propagation of sound in Section 1 of Physics

Selected exercises
Fill in the blanks, multiple choice, calculation
Completion
1. Sound depends on objects________ The sound can be produced in______ 、_______ 、_______ It spreads in matter, but not in space________ It's spreading through the Internet
2. During the dragon boat race, the sound of drums is on the surface of the drum__________ And it is produced by_________ It enters the human ear
3. As shown in figure 3-1-5, figure a shows that a person can make a pleasant drum sound by beating a drum, which indicates that the sound is caused by an object_______________________ The second picture shows that if the air in the glass cover is removed, the bell will not be heard, indicating that the sound transmission depends on the environment________________ ．
4. Don't make a lot of noise when fishing, because fish will be scared away when they hear people's voices, which means that______________ ．
5. If someone shouts at the cliff and hears the echo in 1.2s, the distance from the cliff is about_____ m．（ m/s）
6. as shown in the figure, when the tuning fork is struck, the foam ball will be pressed by the suspended foam plastic. This experiment shows that all the objects that are making sound are making sound___________ ．
7. The students of Dongcheng primary school beat gongs and drums to welcome the recruits into the army. The sound of gongs and drums is due to the surface of gongs and drums_________ Produced, and then through_________ It spread around
8. What is the speed of sound in the air at 15 ℃_________ M / s, Shen Kuo of the Northern Song Dynasty, recorded in his book MengXiBiTan: soldiers sleep on the ground with cowhide and silk quivers when they march and camp, and they can hear the sound of the horses' hooves of the enemies attacking at night as soon as possible______________________________ ．
9. At night, in order to find out the situation as soon as possible, the scouts often put their ears on the ground to listen to the sound of the enemy's horse's hooves, because the sound spreads more quickly in solid than in gas______ ．
10. The propagation speed of sound in the air at room temperature is_____ M / s
11. Usually we hear sound by____________ It's spreading
12. For an aircraft flying at an altitude of 3015m, if the speed of sound propagation in the air is 335m / s, the shortest time for the sound from the aircraft to reach the ground is________ Seconds
13. Sound is caused by the movement of objects_________ And the need for sound transmission_________ ．
14. The condition that the human ear can distinguish the echo from the sound source is the difference between them_____ More than one second
15. To make the flute sound, you must blow it with your mouth to make the flute sound___ Occurrence___ ．
answer
1. Vibration, solid, liquid, gas, vacuum. 2. Vibration, air. 3. Vibration, medium. 4. Liquid (water) can also transmit sound. 5.6. Fill in "bounce", "vibration". 7. Fill in "vibration", "air". 8.340, the speed of sound propagation in the earth is greater than that in the air. 9. Faster. 10.340.11. Air. 12.9.13. Vibration, Medium. 14.0.1.15. Air, vibration
Class A
1. If the echo reaches the human ear more than () seconds later than the original sound, the human ear can distinguish the echo from the original sound
A. 1 second b.0.1 second
C. 0.01 s d.0.001 s
2. Sound travels much faster in solid and liquid than in air
A. Fast B. slow
C. As fast as D. can't compare
3. Sound is produced by the voice body________ It's the result of
A. Motion B. vibration
C. Temperature rise D. volume expansion
Usually the sound we hear comes from ()
A. Electromagnetic wave B. vacuum
C. Air D. eardrum
5. About the transmission of sound, the correct one in the following statement is ()
A. Sound is transmitted in the form of waves by means of media
B. Sound travels at a very small speed in a vacuum
C. The speed of sound propagation in the medium increases with the decrease of temperature
D. The propagation speed of sound in the medium varies with the improvement of quality
6. The time interval between the original sound and the echo should be greater than 0.1s, so the distance between the person and the obstacle should be ()
A. Greater than 17m B. greater than 34m C. less than 17m D. less than 34m
Grade B
7. A blows once at one end of a long enough water pipe, and B listens with an ear tube at the other end
A. One B. most C.3 D.4
8. The correct of the following statement is ()
A. In air, sound travels faster than light
B. Sound travels faster in air than in metal
C. Sound cannot travel in a vacuum
D. Talking in the wilderness is louder than in the house
9. There is a gorge 1200 meters wide with vertical walls on both sides. If a person fires a gun in the gorge, and the interval between the first two echoes is 5 seconds, then the distance between the person and the two walls is (set sound velocity v = 340 m / s)
( )
A. 1025m, 175m, b.600m, 600m
C. 1000m, 200m, d.850m, 350m
answer
1. B 2. A 3. B 4. C 5. A, D. dial: sound must rely on the medium in the process of transmission. There is no medium to transmit sound in vacuum, so a is right and B is wrong. When sound propagates in different media, the propagation speed is different, the fastest in solid and the slowest in gas, so D is not right. 6. A. dial: within the time when people hear the echo, 7. The speed of sound propagation is different in different media. A strikes one end of the water pipe once, causing the pipe to vibrate and make sound. Sound propagates in three ways: one is in the air, one is in the water, and the other is in the iron pipe, In the iron, the speed of transmission is the fastest, followed by the water, and the slowest is in the air. Therefore, the first sound heard is along the iron pipe, the second sound is from the water, and the third sound is from the air. Select C. dial: if the water pipe is very short, the time of sound transmission is very short, we can't distinguish. 8. C.9. A
1. Standing on the bridge, Xiao Ming can see a woman patting clothes with a mallet on the river in the distance. But when she raises the mallet high, Xiao Ming hears the crisp sound of patting clothes. What's the reason? Suppose she patted twice a second, how far is the washing place from the bridge?
2. On the straight double track railway, trains a and B run in the opposite direction at the same speed. 5S after car a whistles, people in car B hear it. Another 40s later, the two cars just meet and miss. Find the distance between the two workshops when car a whistles
3. The speed of sound propagation in the sea is about 1530 M / S. in order to open up a new channel, echo detection instrument is installed on the bottom of the detection ship to detect whether there are hidden reefs under the water. As shown in the figure, the sound signal sent by the detection ship is received by the detector in 0.6 s, and the distance from the obstacle to the detection ship is calculated
4. When a hammers on an object, he hears the sound of the previous hammering
5. A sticks his ear to one end of the long iron pipe, and B knocks on the other end of the iron pipe, and a hears two sounds. If the length of the iron pipe is l, the speed of the iron and the air to transmit the sound is, respectively, and the interval time between the two sounds is calculated
6. The timekeeper at the end of the 100 meter race, after hearing the sound of the starter's gun, counts the time according to the meter. The result is 13.69s. What is the real result of the athlete? (suppose the temperature is 15 ℃ and there is no wind at that time)
answer
1. Seeing clothes is due to the transmission of light, and hearing the sound of clothes is due to the transmission of sound. There is a big difference in the speed of transmission between the two, so there is a time difference that makes us look out of sync. There are two processes of lifting and taking clothes at one time, two times per second. It takes s for each lifting or falling time. A: washing clothes is 85m away from the bridge
2. If the distance between car a and car B is s and the speed of car a and car B is V, the solution is m / s
Dial: this problem seems very complicated. We can simplify the problem as follows: (1) when the sound meets car B, the meeting time is 5S; (2) when car a and car B meet, the meeting time is 45s. The distance between two cars is equal to the distance between two cars when car a whistles
3．
4. A knocks three times per second, i.e. every s, while B hears the sound of the previous knock, i.e. the time taken for the knock to reach B is s, then
5. The time of sound propagation in the air. The time of sound propagation along the steel pipe, then
6. The time taken for sound transmission of 100m
The athlete's vacuum result of 100 meters is
Dial: when the signal bomb of the starting gun explodes, the smoke and sound are formed at the same time, but the speed of light is 900000 times of the speed of sound. In a small distance, the information light (light reflected by smoke) takes a very short time to spread, which can be ignored, while the information sound (gunshot) spreads slowly, which takes a long time to spread. If it is also ignored, it will make the athletes' performance inconsistent with the actual situation

Given that the area of a square is (16-8x + x2) cm2 (x > 4cm), the perimeter of the square is ()
A. （4-x）cmB. （x-4）cmC. （16-4x）cmD. （4x-16）cm

∵ 16-8x + x2 = (4-x) 2, x > 4cm, the side length of the square is (x-4) cm, the perimeter of the square is: 4 (x-4) = 4x-16 (CM), so D

Calculation (1 + 3 + 5 +...) 1990+2001）—（2+4+6+…… How to simplify the calculation

Calculation:
（1+3+5+…… 1990+2001）—（2+4+6+…… 1998+2000）
=1+（3-2）+（5-4）+（7-6）+…… +（2001-2000)
=1+1*1000
=1001 .

Find the following function range y = root sign (lgx + 2)
1. Find the following function range y = root sign lgx + 2
2. If logm 3 ＜ loga 3 ＜ 0, find the condition that m and N satisfy

1. Y = root sign (lgx + 2) because lgx + 2 is in the root sign, when x = 1 / 100, the minimum value of Y is 0; because lgx belongs to R, so lgx + 2 has no maximum value and tends to positive infinity, so y = root sign (lgx + 2) belongs to [0, positive infinity] (x belongs to [1 / 100, positive infinity])
2. Logm3 = (Lg3) / (LGM), logn3 = (Lg3) / (LGN). (1) because Lg3 > 0, 1 / LGM

The ratio of edge length of large square to small square is 5:3, the ratio of bottom area is (), the ratio of surface area is (), and the ratio of volume is ()

The bottom area ratio, surface area ratio and volume ratio are 25:9, 25:9 and 125:27, respectively

How can four and four and four and three be equal to 24

4×(4+3)-4=24

It is known that all items of the sequence {an} are positive numbers, and the first n terms and Sn satisfy 6sn = an ^ 2 + 3an + 2. If A2, A4 and A9 are equal proportion sequence, then the general term of the sequence {an} an =?
RT

6sn = an ^ 2 + 3an + 26sn + 1 = an + 1 ^ 2 + 3an + 1 + 2 are factorized into (an + 1 + an) * (an + 1-an-3) = 0. All items of known sequence {an} are positive numbers, an + 1-an-3) = 0An = 3n-3 + A1, A2, A4, A9 are equal ratio sequence, A4 ^ 2 = A2 * A9 (a + 9) ^ 2 = (a + 3) (a + 24) A1 = 1

There is a rectangle. The ratio of length to width is 7:5. It is known that the circumference of the rectangle is 48CM. What is the area of the rectangle?

48 △ 2 = 24 (CM) 24 × 77 + 5 = 14 (CM) 24 × 57 + 5 = 10 (CM) 14 × 10 = 140 (square cm); answer: the area of this rectangle is 140 square cm