2. In the valley between two parallel cliffs put a gun, 2s after hearing the first shot, and after 1s heard the second shot, the width of the valley is m.
3. A tourist at the bottom of the mountain shouting at a cliff, after 0.4s after hearing the echo, the tourist distance from the cliff m (the speed of sound take 340m / s). Existing two cable cars from the bottom of the mountain at uniform speed to the top of the movement, cable car A relative to the speed of the mountain is greater than the speed of the cable car B relative to the speed of the mountain to the cable car A as a reference, cable car B to the movement. In the game, "ground ball" past the feet of the athletes, the athletes immediately along the trajectory of the soccer ball to catch up, for a while, the soccer ball will be controlled at their feet. This process, the average speed of the athlete (fill in "greater than" "equal to" or "less than") the average speed of the soccer ball.
4. Assuming that there are before and after the two sounds to the human ear, if the two sounds reach the human ear successive time interval greater than (or equal to) 0.1s, the human ear will be able to distinguish between the two sounds. In other words, if the interval between the two sounds is less than 0.1s, the human ear can only hear the sound once. Our school 8th grade extracurricular activities group of students in order to experience the physical phenomenon of sound propagation speed in different media, they asked a student in the water pipeline straight iron pipe (filled with water) on the knock, so that the iron pipe issued a crisp sound, the rest of the students along the iron pipe were in different positions close to the iron pipe ear to listen to the sound. After the end of the experiment, A students said they heard only one sound; B students said they heard two sounds; C students said they heard three sounds. It is known that the propagation speed of sound in the air is v gas = 340m / s, the propagation speed in the water is v water = 1700m / s, the propagation speed in the iron and steel is v iron = 5100m / s. Then the position of the student B to the knocking point of the distance should be in the m range.
5. (1) The maximum distance that the wave source deviates is called the amplitude, which reflects the strength of the source. In the waveform shown in the figure, the amplitude is cm, the wavelength is cm, the distance from point A to the point is one wavelength, and the distance from point B to the point is also one wavelength.
(2) wave source vibration of the time used is called, the figure if the wave source vibration of the time required for a 0.2s, then the frequency of the wave is Hz, the rate of wave propagation for m / s.
6. The speed of sound propagation in the air and the air temperature and air concentration related to the temperature of the air, the air temperature is lower, the concentration of more densely packed when the speed of sound transmission is the more rapid, the church of the outskirts of the city. Residents in the far suburbs of the church often use the clarity of the sound of the chimes to judge changes in the weather. One day, they hear the chimes clearer and clearer, then the weather in the area will be more and more . (fill in "sunny" or "cloudy")
7. A person somewhere between the two mountains (far from the A mountain) shouting, the speed of sound is v, he heard two echoes between the interval is t, if the person to the A mountain of the distance is s, then A, B between the two mountains. The distance between mountain A and B is . (Note: with the letters given in the question)
8. In order to be safe, the train must sound the whistle before entering the tunnel, if the train speed of 72km / h, the driver in the whistle after 2s heard from the tunnel mouth cliffs reflecting echoes, then the train from the mouth of the tunnel at the time of sounding the whistle m, the sound is known to the speed of the air is 340m / s.
9 Xiaomao made a flute with a straw in the pipe. There are five holes in the straw, one of which is a blow hole. One of the five holes is a blowhole. If you blow into the hole with your mouth, the sound of the flute is produced by the column of air inside the straw. If you hold your finger over the other holes and blow the flute, you can hear different sounds, which mainly change the sound of the flute. If you blow the flute late at night, the sound of the flute belongs to the...
10The sound of music has three elements: pitch, loudness and timbre. In our daily lives, we often say that the sound "deafening", which refers to its great; can distinguish the singer Jay Chou's voice, mainly based on the sound of the judgment.
11 familiar with the singer or classmates, you will know who you are listening to, you are based on his (her) voice to identify. One of the boys in the class has a big voice, and that's because he has a big voice.
12 The sound of car horns is produced by the horn, the city banned honking is to eliminate noise from the place; if the highway and residential construction of a glass wall between the people in the house (fill in the can or can not) to hear the highway car horns.
13 summer evening, some middle-aged and elderly people like to dance, beautiful dance music is due to the speaker cone issued by the sound is transmitted into the human ear, in order not to affect the lives of the surrounding residents and rest, some people suggest dancing will be the volume of the speakers down, which is in the place of attenuation of noise.
14 Howler monkeys are one of the world's loudest animals, it is a thunderous roar to warn other animals not to encroach on its territory. The word "thunderous" describes the character of the sound. People can recognize the call of a howler monkey by the character of its sound.
15 "China's best song" competition site, the singer plays the guitar constantly with fingers to control the length of the strings, the purpose of doing so is to change the sound; the audience on the scene will turn the phone into a mute state, the purpose is to reduce the noise．
16" Bluefin tuna "is the United States used to search for the missing Malaysia Airlines aircraft MH370 underwater autonomous navigation. "Bluefin tuna" works by emitting sound waves to scan the seabed and receiving reflected sound waves from objects, and using "acoustic shadows" to determine the height of the object. If the reflected sound wave is received 6s after the sound wave is emitted, the distance of "bluefin tuna" from the seabed is meters. (The speed of sound in seawater is 1531 meters per second)
17 Square dancing as a new form of recreation, in recent years in the country "blossomed". But the huge noise makes the square dance into a headache for people "disturbing dance", mainly because it sends out the sound of the (fill in the characteristics of the sound) large, affecting the neighborhood residents rest and study. For this phenomenon. Please put forward a reasonable proposal: .
18 Often watch CCTV "News" program audience, just listen to the sound to know who is broadcasting, which is the audience according to the sound of the judgment; most people can hear the sound of the frequency range of Hz ~ 20,000Hz: close to the residential areas of the highway on both sides of the general installation of noise walls, which is in the sound attenuation of noise.
19 The sound wall is installed on both sides of the highway near the residential area.
19 height 170cm of someone's eyes in the top of his head at 10cm below, in order to be able to see their own full-body image from a vertically suspended plane mirror, he purchased a plane mirror should be at least the height of cm, and the mirror is suspended vertically, should be made to make the upper end in the top of the head of the person at the bottom of the cm at the same level.
20 In a calm lake over the air quality monitoring of a balloon (at rest). An instrument placed 20 meters above the surface of the lake measures the elevation angle of the balloon to be 30°, and the pitch angle of the balloon's virtual image in the water is measured to be 60°, then the height of the balloon from the surface of the lake is meters.
Not difficult, depending on your level
Space did not hit the understanding