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The length of a line is 450m, and the speed is 90m per minute. In order to convey an order, the correspondent rushes from the end of the line to the head of the line, and then rushes back to the end of the line immediately. His speed is 3M per second. Question: (1) how long does it take for the correspondent to go from the end of the line to the end of the line? (2) What is the distance and displacement of the correspondent?
(1) According to the meaning of the question, l = 450m, V1 = 9069m / S = 1.5m/s, V2 = 3m / s, the correspondent's speed relative to the team is v = v2-v1 = 3m / s-1.5m/s = 1.5m/s in the process of running from the end of the team to the head of the team, so the time required for the correspondent to run from the end of the team to the head of the team is T1 = LV = 4501.5s = 300s, and the correspondent is relatively slow in the process of running from the head of the team to the end of the team The speed of the team is v ′ = V1 + V2 = 1.5m/s + 3m / S = 4.5m/s, so the time required for the correspondent to run from the front to the back of the team is T2 = LV ′ = 4504.5s = 100s, so the total time required for the correspondent to leave and return to the back of the team is t 1 + T2 = 300s + 100s = 400s. (2) the distance between the messenger's return and departure, that is, the distance of the team in this period of time is s = v1t = 3m / s × 400s = 1200m Answer: (1) it takes 400s for the correspondent to leave the team and return to the end of the line; (2) the distance of the correspondent is 1200m and the displacement is 450m
There is a column of numbers 1,1,2,4,7,13,24,44,81. Starting from the fourth number, each number is the sum of its first three numbers, so what is the 100th number?
It's odd or even
Look at the law
Single double double single double double
100 / 4 = 25 (exclusive)
So even numbers
Hope to help you!
2 + 3 of 2 = 2 square * 3 of 2.3 + 3 of 8 = 3 square * 8 of 3.4 + 15 of 4. If 9 + a of B, then a + B =?
Your topic is incomplete. According to reasoning, the complete topic should be:
2 + 3 of 2 = 2 square * 3 of 2.3 + 8 of 3 = 3 square * 8 of 3.4 + 15 of 4 = 4 square * 15 of 4. If 9 + a of B = 9 square * a of B, then a + B =?
The answer is:
First, according to the rule B = 9
9 + 9 / a = 9 square * 9 / A
9A + 9 = 9 cubic meters
a = 80
a + b = 89
What are the knowledge points in the first chapter of physics in grade two
The first chapter summarizes the knowledge of sound phenomenon
1. Sound generation: produced by the vibration of an object. When the vibration stops, the sound stops
2. Sound transmission: sound is transmitted by medium. Vacuum cannot transmit sound. Usually, the sound we hear is transmitted by air
3. Speed of sound: in air, the speed is 340m / s. sound travels faster in solid than in liquid, and in liquid than in air
4. The distance can be measured by echo: S = 1 / 2vt
5. Three characteristics of musical sound: tone, loudness and timbre. (1) tone refers to the height of the sound, which is related to the frequency of the speaker. (2) loudness refers to the size of the sound, which is related to the amplitude of the speaker and the distance between the source and the listener
6. Ways to reduce noise: (1) at the sound source; (2) in the process of transmission; (3) at the human ear
7. Audible sound: sound wave with frequency between 20Hz and 20000hz; ultrasonic wave: sound wave with frequency higher than 20000hz; infrasound wave: sound wave with frequency lower than 20Hz
8. Ultrasonic features: good directivity, strong penetration, concentrated sound energy. Specific applications include: sonar, B-ultrasound, ultrasonic speed detector, ultrasonic cleaner, ultrasonic welder, etc
9. Characteristics of infrasound wave: it can spread far away, easily bypass obstacles, and go through all directions. Infrasound wave of a certain intensity will cause harm to human body, even damage mechanical buildings, etc. it is mainly produced in the nature of volcanic eruptions, tsunamis, earthquakes, etc. in addition, human made rocket launch, aircraft flight, Mercedes Benz of trains and cars, nuclear explosion, etc. can also produce infrasound wave
A bag contains four different colors of balls, including 10 red balls, 9 blue balls, 8 yellow balls and 7 white balls. Only when someone closes his eyes and takes at least () balls out of the bag can he guarantee that there are four colors of balls
Take out the red, blue and yellow
And then take another sacrifice. It's all in it
10+9+8+1=28
A: take out at least 28 balls to ensure that the four colors of the ball have
How many square meters is 3000 feet
Foot is a unit of length, but square foot is a unit of area
3000 feet = 278.7 square meters
If pile a and pile B transport 9 tons of coal to pile B, pile a will be 3 tons less than pile B. now that both piles transport the same number of tons, the ratio of tons left in pile a and pile B is 20:17. How many tons of coal is left in pile a?
9*2-3=15
Pile a is 15 tons more than pile B
At the same time, after several tons are transported away, pile a is still 15 tons more than pile B
So there is still a pile of armor left
15 ÷ (20-17) * 20 = 100 tons
A: at this time, the remaining coal in pile a is 100 tons
If you have any other questions, please take this question and ask for help,
One sixth of the number a is equal to one fourth of the number B. the ratio of a to B is (). If a is 15 more than B, the ratio of a to B is ()
One sixth of the number of a is equal to one fourth of the number of B. the ratio of a to B is 2:3. If a is 15 more than B, the ratio of a to B is 3:2
How much sodium hydroxide and water are needed to prepare 500 ml 10% sodium hydroxide solution (density is 1.1 g / cm3)?
To prepare 500ml (500cm3) sodium hydroxide solution with 10% mass fraction, the mass of sodium hydroxide is 500cm3 × 1.1g/cm3 × 10% = 55g; the mass of water is 500cm3 × 1.1g/cm3-55g = 495G. A: the mass of sodium hydroxide and water are 55g and 495G respectively
(unit 3, cuboid and cube) Name:________ Results:________
1、 I can fill in (22 points) 1. Use (8) cubes with the edge length of 1 decimeter to form a large cube with the edge length of 1 meter. 2. The characteristics of numbers that can be divisible by 2 and 5 at the same time (natural numbers with zero digits). In the natural numbers of 3, 1-10, odd numbers are (1, 3, 5, 7, 9), even numbers are (2, 4, 6, 8
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